Guide to industrial control systems (ics) security

Special Publication 800-82
Guide to Industrial Control
Systems (ICS) Security
Supervisory Control and Data Acquisition (SCADA) systems, Distributed
Control Systems (DCS), and other control system configurations such
as Programmable Logic Controllers (PLC)
Recommendations of the National Institute
of Standards and Technology
KeithStouffer
JoeFalco
KarenScarfone

NIST Special Publication 800-82 Guide to Industrial Control Systems (ICS)
Security
Supervisory Control and Data Acquisition (SCADA)
systems, Distributed Control Systems (DCS), and
other control system configurations such as
Programmable Logic Controllers (PLC)
Recommendations of the National
Institute of Standards and Technology
Computer Security Division
Information Technology Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899-8930
Intelligent Systems Division
Engineering Laboratory
Gaithersburg, MD 20899-8930
June 2011
U.S. Department of Commerce
Gary Locke, Secretary
Patrick Gallagher, Director
C O M P U T E R S E C U R I T Y

GUIDE TO INDUSTRIAL CONTROL SYSTEMS (ICS) SECURITY
Reports on Computer Systems Technology
The Information Technology Laboratory (ITL) at the National Institute of Standards and Technology
(NIST) promotes the U.S. economy and public welfare by providing technical leadership for the nation’s
measurement and standards infrastructure. ITL develops tests, test methods, reference data, proof of
concept implementations, and technical analysis to advance the development and productive use of
information technology. ITL’s responsibilities include the development of technical, physical,
administrative, and management standards and guidelines for the cost-effective security and privacy of
sensitive unclassified information in Federal computer systems. This Special Publication 800-series
reports on ITL’s research, guidance, and outreach efforts in computer security and its collaborative
activities with industry, government, and academic organizations.
Certain commercial entities, equipment, or materials may be identified in this
document in order to describe an experimental procedure or concept adequately.
Such identification is not intended to imply recommendation or endorsement by the
National Institute of Standards and Technology, nor is it intended to imply that the
entities, materials, or equipment are necessarily the best available for the purpose.
National Institute of Standards and Technology Special Publication 800-82
Natl. Inst. Stand. Technol. Spec. Publ. 800-82, 155 pages (June 2011)
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Acknowledgments
The authors, Keith Stouffer, Joe Falco, and Karen Scarfone of the National Institute of Standards and
Technology (NIST), wish to thank their colleagues who reviewed drafts of this document and contributed
to its technical content. The authors would particularly like to acknowledge Tim Grance, Ron Ross, Stu
Katzke, and Freemon Johnson of NIST for their keen and insightful assistance throughout the
development of the document. The authors also gratefully acknowledge and appreciate the many
contributions from the public and private sectors whose thoughtful and constructive comments improved
the quality and usefulness of this publication. The authors would particularly like to thank the members
of ISA99. The authors would also like to thank the UK National Centre for the Protection of National
Infrastructure (CPNI)) for allowing portions of the Good Practice Guide on Firewall Deployment for
SCADA and Process Control Network to be used in this document as well as ISA for allowing portions of
the ANSI/ISA99 Standards to be used in this document.

Table of Contents
Executive Summary..............................................................................................................ES-1
1. Introduction ......................................................................................................................1-1
1.1 Authority...................................................................................................................1-1
1.2 Purpose and Scope .................................................................................................1-1
1.3 Audience..................................................................................................................1-1
1.4 Document Structure.................................................................................................1-2
2. Overview of Industrial Control Systems........................................................................2-1
2.1 Overview of SCADA, DCS, and PLCs .....................................................................2-1
2.2 ICS Operation ..........................................................................................................2-2
2.3 Key ICS Components ..............................................................................................2-3
2.3.1 Control Components.....................................................................................2-4
2.3.2 Network Components...................................................................................2-5
2.4 SCADA Systems......................................................................................................2-6
2.5 Distributed Control Systems ..................................................................................2-10
2.6 Programmable Logic Controllers ...........................................................................2-12
2.7 Industrial Sectors and Their Interdependencies ....................................................2-13
3. ICS Characteristics, Threats and Vulnerabilities ..........................................................3-1
3.1 Comparing ICS and IT Systems ..............................................................................3-1
3.2 Threats.....................................................................................................................3-5
3.3 Potential ICS Vulnerabilities.....................................................................................3-6
3.3.1 Policy and Procedure Vulnerabilities............................................................3-7
3.3.2 Platform Vulnerabilities.................................................................................3-8
3.3.3 Network Vulnerabilities...............................................................................3-12
3.4 Risk Factors...........................................................................................................3-14
3.4.1 Standardized Protocols and Technologies.................................................3-15
3.4.2 Increased Connectivity ...............................................................................3-15
3.4.3 Insecure and Rogue Connections ..............................................................3-16
3.4.4 Public Information.......................................................................................3-16
3.5 Possible Incident Scenarios...................................................................................3-17
3.6 Sources of Incidents ..............................................................................................3-18
3.7 Documented Incidents ...........................................................................................3-19
4. ICS Security Program Development and Deployment..................................................4-1
4.1 Business Case for Security......................................................................................4-1
4.1.1 Benefits.........................................................................................................4-1
4.1.2 Potential Consequences...............................................................................4-2
4.1.3 Key Components of the Business Case.......................................................4-3
4.1.4 Resources for Building Business Case ........................................................4-4
4.1.5 Presenting the Business Case to Leadership...............................................4-4
4.2 Developing a Comprehensive Security Program .....................................................4-4
4.2.1 Senior Management Buy-in..........................................................................4-5
4.2.2 Build and Train a Cross-Functional Team ....................................................4-5
4.2.3 Define Charter and Scope............................................................................4-6
4.2.4 Define ICS Specific Security Policies and Procedures.................................4-6
4.2.5 Define and Inventory ICS Systems and Networks Assets............................4-6
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4.2.6 Perform Risk and Vulnerability Assessment.................................................4-7
4.2.7 Define the Mitigation Controls ......................................................................4-8
4.2.8 Provide Training and Raise Security Awareness .........................................4-9
5. Network Architecture.......................................................................................................5-1
5.1 Firewalls...................................................................................................................5-1
5.2 Logically Separated Control Network.......................................................................5-3
5.3 Network Segregation ...............................................................................................5-3
5.3.1 Dual-Homed Computer/Dual Network Interface Cards (NIC).......................5-3
5.3.2 Firewall between Corporate Network and Control Network..........................5-4
5.3.3 Firewall and Router between Corporate Network and Control Network.......5-6
5.3.4 Firewall with DMZ between Corporate Network and Control Network..........5-7
5.3.5 Paired Firewalls between Corporate Network and Control Network ............5-9
5.3.6 Network Segregation Summary..................................................................5-10
5.4 Recommended Defense-in-Depth Architecture .....................................................5-10
5.5 General Firewall Policies for ICS ...........................................................................5-11
5.6 Recommended Firewall Rules for Specific Services..............................................5-13
5.6.1 Domain Name System (DNS).....................................................................5-14
5.6.2 Hypertext Transfer Protocol (HTTP)...........................................................5-14
5.6.3 FTP and Trivial File Transfer Protocol (TFTP) ...........................................5-14
5.6.4 Telnet..........................................................................................................5-14
5.6.5 Simple Mail Transfer Protocol (SMTP) .......................................................5-14
5.6.6 Simple Network Management Protocol (SNMP) ........................................5-15
5.6.7 Distributed Component Object Model (DCOM) ..........................................5-15
5.6.8 SCADA and Industrial Protocols.................................................................5-15
5.7 Network Address Translation (NAT) ......................................................................5-15
5.8 Specific ICS Firewall Issues...................................................................................5-16
5.8.1 Data Historians...........................................................................................5-16
5.8.2 Remote Support Access.............................................................................5-16
5.8.3 Multicast Traffic ..........................................................................................5-17
5.9 Single Points of Failure..........................................................................................5-17
5.10 Redundancy and Fault Tolerance..........................................................................5-18
5.11 Preventing Man-in-the-Middle Attacks ...................................................................5-18
6. ICS Security Controls ......................................................................................................6-1
6.1 Management Controls..............................................................................................6-1
6.1.1 Security Assessment and Authorization.......................................................6-2
6.1.2 Planning........................................................................................................6-2
6.1.3 Risk Assessment..........................................................................................6-3
6.1.4 System and Services Acquisition .................................................................6-5
6.1.5 Program Management..................................................................................6-6
6.2 Operational Controls................................................................................................6-6
6.2.1 Personnel Security .......................................................................................6-7
6.2.2 Physical and Environmental Protection........................................................6-7
6.2.3 Contingency Planning.................................................................................6-11
6.2.4 Configuration Management ........................................................................6-13
6.2.5 Maintenance...............................................................................................6-14
6.2.6 System and Information Integrity................................................................6-14
6.2.7 Media Protection.........................................................................................6-18
6.2.8 Incident Response......................................................................................6-18
6.2.9 Awareness and Training.............................................................................6-21
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6.3 Technical Controls .................................................................................................6-22
6.3.1 Identification and Authentication.................................................................6-22
6.3.2 Access Control ...........................................................................................6-27
6.3.3 Audit and Accountability .............................................................................6-31
6.3.4 System and Communications Protection....................................................6-32
List of Appendices
Appendix A— Acronyms and Abbreviations .......................................................................A-1
Appendix B— Glossary of Terms..........................................................................................B-1
Appendix C— Current Activities in Industrial Control System Security ...........................C-1
Appendix D— Emerging Security Capabilities ....................................................................D-1
Appendix E— Industrial Control Systems in the FISMA Paradigm.................................... E-1
Appendix F— References ...................................................................................................... F-1
List of Figures
Figure 2-1. ICS Operation.........................................................................................................2-3
Figure 2-2. SCADA System General Layout.............................................................................2-7
Figure 2-3. Basic SCADA Communication Topologies.............................................................2-8
Figure 2-4. Large SCADA Communication Topology ...............................................................2-8
Figure 2-5. SCADA System Implementation Example (Distribution Monitoring and Control)...2-9
Figure 2-6. SCADA System Implementation Example (Rail Monitoring and Control).............2-10
Figure 2-7. DCS Implementation Example .............................................................................2-11
Figure 2-8. PLC Control System Implementation Example ....................................................2-12
Figure 3-1. Industrial Security Incidents by Year ....................................................................3-19
Figure 5-1. Firewall between Corporate Network and Control Network....................................5-4
Figure 5-2. Firewall and Router between Corporate Network and Control Network.................5-6
Figure 5-3. Firewall with DMZ between Corporate Network and Control Network....................5-7
Figure 5-4. Paired Firewalls between Corporate Network and Control Network.......................5-9
Figure 5-5. CSSP Recommended Defense-In-Depth Architecture.........................................5-11
Figure E-1. Risk Management Framework .............................................................................. E-3
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List of Tables
Table 3-1. Summary of IT System and ICS Differences ...........................................................3-3
Table 3-2. Adversarial Threats to ICS.......................................................................................3-5
Table 3-3. Policy and Procedure Vulnerabilities .......................................................................3-7
Table 3-4. Platform Configuration Vulnerabilities......................................................................3-8
Table 3-5. Platform Hardware Vulnerabilities .........................................................................3-10
Table 3-6. Platform Software Vulnerabilities...........................................................................3-10
Table 3-7. Platform Malware Protection Vulnerabilities ..........................................................3-11
Table 3-8. Network Configuration Vulnerabilities....................................................................3-12
Table 3-9. Network Hardware Vulnerabilities..........................................................................3-13
Table 3-10. Network Perimeter Vulnerabilities........................................................................3-13
Table 3-11. Network Monitoring and Logging Vulnerabilities..................................................3-14
Table 3-12. Communication Vulnerabilities ............................................................................3-14
Table 3-13. Wireless Connection Vulnerabilities ....................................................................3-14
Table 4-1. Suggested Actions for ICS Vulnerability Assessments............................................4-8
Table E-1. Possible Definitions for ICS Impact Levels Based on ISA99.................................. E-5
Table E-2. Possible Definitions for ICS Impact Levels Based on Product Produced, Industry
and Security Concerns...................................................................................................... E-5

Executive Summary
This document provides guidance for establishing secure industrial control systems (ICS). These ICS,
which include supervisory control and data acquisition (SCADA) systems, distributed control systems
(DCS), and other control system configurations such as skid-mounted Programmable Logic Controllers
(PLC) are often found in the industrial control sectors. ICS are typically used in industries such as
electric, water and wastewater, oil and natural gas, transportation, chemical, pharmaceutical, pulp and
paper, food and beverage, and discrete manufacturing (e.g., automotive, aerospace, and durable goods.)
SCADA systems are generally used to control dispersed assets using centralized data acquisition and
supervisory control. DCS are generally used to control production systems within a local area such as a
factory using supervisory and regulatory control. PLCs are generally used for discrete control for specific
applications and generally provide regulatory control. These control systems are vital to the operation of
the U.S. critical infrastructures that are often highly interconnected and mutually dependent systems. It is
important to note that approximately 90 percent of the nation's critical infrastructures are privately owned
and operated. Federal agencies also operate many of the ICS mentioned above; other examples include
air traffic control and materials handling (e.g., Postal Service mail handling.) This document provides an
overview of these ICS and typical system topologies, identifies typical threats and vulnerabilities to these
systems, and provides recommended security countermeasures to mitigate the associated risks.
Initially, ICS had little resemblance to traditional information technology (IT) systems in that ICS were
isolated systems running proprietary control protocols using specialized hardware and software. Widely
available, low-cost Internet Protocol (IP) devices are now replacing proprietary solutions, which increases
the possibility of cyber security vulnerabilities and incidents. As ICS are adopting IT solutions to
promote corporate business systems connectivity and remote access capabilities, and are being designed
and implemented using industry standard computers, operating systems (OS) and network protocols, they
are starting to resemble IT systems. This integration supports new IT capabilities, but it provides
significantly less isolation for ICS from the outside world than predecessor systems, creating a greater
need to secure these systems. While security solutions have been designed to deal with these security
issues in typical IT systems, special precautions must be taken when introducing these same solutions to
ICS environments. In some cases, new security solutions are needed that are tailored to the ICS
environment.
Although some characteristics are similar, ICS also have characteristics that differ from traditional
information processing systems. Many of these differences stem from the fact that logic executing in ICS
has a direct affect on the physical world. Some of these characteristics include significant risk to the
health and safety of human lives and serious damage to the environment, as well as serious financial
issues such as production losses, negative impact to a nation’s economy, and compromise of proprietary
information. ICS have unique performance and reliability requirements and often use operating systems
and applications that may be considered unconventional to typical IT personnel. Furthermore, the goals
of safety and efficiency sometimes conflict with security in the design and operation of control systems.
Originally, ICS implementations were susceptible primarily to local threats because many of their
components were in physically secured areas and the components were not connected to IT networks or
systems. However, the trend toward integrating ICS systems with IT networks provides significantly less
isolation for ICS from the outside world than predecessor systems, creating a greater need to secure these
systems from remote, external threats. Also, the increasing use of wireless networking places ICS
implementations at greater risk from adversaries who are in relatively close physical proximity but do not
have direct physical access to the equipment. Threats to control systems can come from numerous
sources, including hostile governments, terrorist groups, disgruntled employees, malicious intruders,
complexities, accidents, natural disasters as well as malicious or accidental actions by insiders. ICS
security objectives typically follow the priority of availability, integrity and confidentiality, in that order.
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Possible incidents an ICS may face include the following:
Blocked or delayed flow of information through ICS networks, which could disrupt ICS operation
Unauthorized changes to instructions, commands, or alarm thresholds, which could damage, disable,
or shut down equipment, create environmental impacts, and/or endanger human life
Inaccurate information sent to system operators, either to disguise unauthorized changes, or to cause
the operators to initiate inappropriate actions, which could have various negative effects
ICS software or configuration settings modified, or ICS software infected with malware, which could
have various negative effects
Interference with the operation of safety systems, which could endanger human life.
Major security objectives for an ICS implementation should include the following:
Restricting logical access to the ICS network and network activity. This includes using a
demilitarized zone (DMZ) network architecture with firewalls to prevent network traffic from passing
directly between the corporate and ICS networks, and having separate authentication mechanisms and
credentials for users of the corporate and ICS networks. The ICS should also use a network topology
that has multiple layers, with the most critical communications occurring in the most secure and
reliable layer.
Restricting physical access to the ICS network and devices. Unauthorized physical access to
components could cause serious disruption of the ICS’s functionality. A combination of physical
access controls should be used, such as locks, card readers, and/or guards.
Protecting individual ICS components from exploitation. This includes deploying security
patches in as expeditious a manner as possible, after testing them under field conditions; disabling all
unused ports and services; restricting ICS user privileges to only those that are required for each
person’s role; tracking and monitoring audit trails; and using security controls such as antivirus
software and file integrity checking software where technically feasible to prevent, deter, detect, and
mitigate malware.
Maintaining functionality during adverse conditions. This involves designing the ICS so that each
critical component has a redundant counterpart. Additionally, if a component fails, it should fail in a
manner that does not generate unnecessary traffic on the ICS or other networks, or does not cause
another problem elsewhere, such as a cascading event.
Restoring system after an incident. Incidents are inevitable and an incident response plan is
essential. A major characteristic of a good security program is how quickly a system can be
recovered after an incident has occurred.
To properly address security in an ICS, it is essential for a cross-functional cyber security team to share
their varied domain knowledge and experience to evaluate and mitigate risk to the ICS. The cyber
security team should consist of a member of the organization’s IT staff, control engineer, control system
operator, network and system security expert, a member of the management staff, and a member of the
physical security department at a minimum. For continuity and completeness, the cyber security team
should consult with the control system vendor and/or system integrator as well. The cyber security team
should report directly to site management (e.g., facility superintendent) or the company’s CIO/CSO, who
in turn, accepts complete responsibility and accountability for the cyber security of the ICS. An effective
cyber security program for an ICS should apply a strategy known as “defense-in-depth”, layering security
mechanisms such that the impact of a failure in any one mechanism is minimized.
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In a typical ICS this means a defense-in-depth strategy that includes:
Developing security policies, procedures, training and educational material that apply specifically
to the ICS.
Considering ICS security policies and procedures based on the Homeland Security Advisory
System Threat Level, deploying increasingly heightened security postures as the Threat Level
increases.
Addressing security throughout the lifecycle of the ICS from architecture design to procurement to
installation to maintenance to decommissioning.
Implementing a network topology for the ICS that has multiple layers, with the most critical
communications occurring in the most secure and reliable layer.
Providing logical separation between the corporate and ICS networks (e.g., stateful inspection
firewall(s) between the networks).
Employing a DMZ network architecture (i.e., prevent direct traffic between the corporate and ICS
networks).
Ensuring that critical components are redundant and are on redundant networks.
Designing critical systems for graceful degradation (fault tolerant) to prevent catastrophic
cascading events.
Disabling unused ports and services on ICS devices after testing to assure this will not impact ICS
operation.
Restricting physical access to the ICS network and devices.
Restricting ICS user privileges to only those that are required to perform each person’s job (i.e.,
establishing role-based access control and configuring each role based on the principle of least
privilege).
Considering the use of separate authentication mechanisms and credentials for users of the ICS
network and the corporate network (i.e., ICS network accounts do not use corporate network user
accounts).
Using modern technology, such as smart cards for Personal Identity Verification (PIV).
Implementing security controls such as intrusion detection software, antivirus software and file
integrity checking software, where technically feasible, to prevent, deter, detect, and mitigate the
introduction, exposure, and propagation of malicious software to, within, and from the ICS.
Applying security techniques such as encryption and/or cryptographic hashes to ICS data storage
and communications where determined appropriate.
Expeditiously deploying security patches after testing all patches under field conditions on a test
system if possible, before installation on the ICS.
Tracking and monitoring audit trails on critical areas of the ICS.
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NIST has created the Industrial Control System Security project1
in cooperation with the public and
private sector ICS community to develop specific guidance on the application of the security controls in
NIST SP 800-53, Recommended Security Controls for Federal Information Systems and Organizations to
ICS.
While most controls in Appendix F of NIST SP 800-53 are applicable to ICS as written, several controls
did require ICS-specific interpretation and/or augmentation by adding one or more of the following to the
control:
ICS Supplemental Guidance provides organizations with additional information on the
application of the security controls and control enhancements in Appendix F of NIST SP 800-
53 to ICS and the environments in which these specialized systems operate. The Supplemental
Guidance also provides information as to why a particular security control or control
enhancement may not be applicable in some ICS environments and may be a candidate for
tailoring (i.e., the application of scoping guidance and/or compensating controls). ICS
Supplemental Guidance does not replace the original Supplemental Guidance in Appendix F of
NIST SP 800-53.
ICS Enhancements (one or more) that provide enhancement augmentations to the original
control that may be required for some ICS
ICS Enhancement Supplemental Guidance that provides guidance on how the control
enhancement applies, or does not apply, in ICS environments.
This ICS-specific guidance is included in NIST SP 800-53, Revision 3, Appendix I: Industrial Control
Systems – Security Controls, Enhancements, and Supplemental Guidance. Section 6 of this document
also provides initial guidance on how 800-53 security controls apply to ICS. Initial recommendations and
guidance, if available, are provided in an outlined box for each section. NIST is planning a December
2011 update to NIST SP 800-53 (NIST SP 800-53, Revision 4), including an update of current security
controls, control enhancements, supplemental guidance, as well as tailoring and supplementation
guidance, in the area of industrial control systems.
Additionally, Appendix C of this document provides an overview of the many activities currently ongoing
among Federal organizations, standards organizations, industry groups, and automation system vendors to
make available recommended practices in the area of ICS security.
The most successful method for securing an ICS is to gather industry recommended practices and
engage in a proactive, collaborative effort between management, the controls engineer and operator, the
IT organization, and a trusted automation advisor. This team should draw upon the wealth of
information available from ongoing federal government, industry groups, vendor and standards
organizational activities listed in Appendix C.
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The Industrial Control System Security Project Web site is located at: http://csrc.nist.gov/groups/SMA/fisma/ics/

1. Introduction
1.1 Authority
The National Institute of Standards and Technology (NIST) developed this document in furtherance of its
statutory responsibilities under the Federal Information Security Management Act (FISMA) of 2002,
Public Law 107-347 and Homeland Security Presidential Directive 7 (HSPD-7) of 2003.
NIST is responsible for developing standards and guidelines, including minimum requirements, for
providing adequate information security for all agency operations and assets, but such standards and
guidelines shall not apply to national security systems. This guideline is consistent with the requirements
of the Office of Management and Budget (OMB) Circular A-130, Section 8b(3), “Securing Agency
Information Systems,” as analyzed in A-130, Appendix IV: Analysis of Key Sections. Supplemental
information is provided in A-130, Appendix III.
This guideline has been prepared for use by Federal agencies. It may be used by nongovernmental
organizations on a voluntary basis and is not subject to copyright, though attribution is desired.
Nothing in this document should be taken to contradict standards and guidelines made mandatory and
binding on Federal agencies by the Secretary of Commerce under statutory authority, nor should these
guidelines be interpreted as altering or superseding the existing authorities of the Secretary of Commerce,
Director of the OMB, or any other Federal official.
1.2 Purpose and Scope
The purpose of this document is to provide guidance for securing industrial control systems (ICS),
including supervisory control and data acquisition (SCADA) systems, distributed control systems (DCS),
and other systems performing control functions. The document provides an overview of ICS and typical
system topologies, identifies typical threats and vulnerabilities to these systems, and provides
recommended security countermeasures to mitigate the associated risks. Because there are many different
types of ICS with varying levels of potential risk and impact, the document provides a list of many
different methods and techniques for securing ICS. The document should not be used purely as a
checklist to secure a specific system. Readers are encouraged to perform a risk-based assessment on their
systems and to tailor the recommended guidelines and solutions to meet their specific security, business
and operational requirements.
The scope of this document includes ICS that are typically used in the electric, water and wastewater, oil
and natural gas, chemical, pharmaceutical, pulp and paper, food and beverage, and discrete manufacturing
(automotive, aerospace, and durable goods) industries.
1.3 Audience
This document covers details specific to ICS. The document is technical in nature; however, it provides
the necessary background to understand the topics that are discussed.
The intended audience is varied and includes the following:
Control engineers, integrators, and architects who design or implement secure ICS
System administrators, engineers, and other information technology (IT) professionals who
administer, patch, or secure ICS
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1-2
Security consultants who perform security assessments and penetration testing of ICS
Managers who are responsible for ICS
Senior management who are trying to understand implications and consequences as they justify and
apply an ICS cyber security program to help mitigate impacts to business functionality
Researchers and analysts who are trying to understand the unique security needs of ICS
Vendors that are developing products that will be deployed as part of an ICS
Readers of this document are assumed to be familiar with general computer security concepts,
communication protocols such as those used in networking and with using Web-based methods for
retrieving information.
1.4 Document Structure
The remainder of this guide is divided into the following major sections:
Section 2 provides an overview of SCADA and other ICS as well as their importance as a rationale
for the need for security.
Section 3 provides a discussion of differences between ICS and IT systems, as well as threats,
vulnerabilities and incidents.
Section 4 provides an overview of the development and deployment of an ICS security program to
mitigate the risk of the vulnerabilities identified in Section 3.
Section 5 provides recommendations for integrating security into network architectures typically
found in ICS, with an emphasis on network segregation practices.
Section 6 provides a summary of the management, operational, and technical controls identified in
NIST Special Publication 800-53, Recommended Security Controls for Federal Information Systems
and Organizations, and provides initial guidance on how these security controls apply to ICS.
The guide also contains several appendices with supporting material, as follows:
Appendix A provides a list of acronyms and abbreviations used in this document.
Appendix B provides a glossary of terms used in this document.
Appendix C provides a list and short description of some of the current activities in ICS security.
Appendix D provides a list of some emerging security capabilities being developed for ICS.
Appendix E provides an overview of the FISMA implementation project and supporting documents,
and the relevancy of FISMA to ICS.
Appendix F provides a list of references used in the development of this document.

2. Overview of Industrial Control Systems
Industrial control system (ICS) is a general term that encompasses several types of control systems,
including supervisory control and data acquisition (SCADA) systems, distributed control systems (DCS),
and other control system configurations such as skid-mounted Programmable Logic Controllers (PLC)
often found in the industrial sectors and critical infrastructures. ICS are typically used in industries such
as electrical, water and wastewater, oil and natural gas, chemical, transportation, pharmaceutical, pulp and
paper, food and beverage, and discrete manufacturing (e.g., automotive, aerospace, and durable goods.)
These control systems are critical to the operation of the U.S. critical infrastructures that are often highly
interconnected and mutually dependent systems. It is important to note that approximately 90 percent of
the nation's critical infrastructures are privately owned and operated. Federal agencies also operate many
of the industrial processes mentioned above; other examples include air traffic control and materials
handling (e.g., Postal Service mail handling.) This section provides an overview of SCADA, DCS, and
PLC systems, including typical architectures and components. Several diagrams are presented to depict
the network connections and components typically found on each system to facilitate the understanding of
these systems. Keep in mind that actual implementations of ICS may be hybrids that blur the line
between DCS and SCADA systems by incorporating attributes of both. Please note that the diagrams in
this section do not represent a secure ICS. Architecture security and security controls are discussed in
Section 5 and Section 6 of this document respectively.
2.1 Overview of SCADA, DCS, and PLCs
SCADA systems are highly distributed systems used to control geographically dispersed assets, often
scattered over thousands of square kilometers, where centralized data acquisition and control are critical
to system operation. They are used in distribution systems such as water distribution and wastewater
collection systems, oil and natural gas pipelines, electrical power grids, and railway transportation
systems. A SCADA control center performs centralized monitoring and control for field sites over long-
distance communications networks, including monitoring alarms and processing status data. Based on
information received from remote stations, automated or operator-driven supervisory commands can be
pushed to remote station control devices, which are often referred to as field devices. Field devices
control local operations such as opening and closing valves and breakers, collecting data from sensor
systems, and monitoring the local environment for alarm conditions.
DCS are used to control industrial processes such as electric power generation, oil refineries, water and
wastewater treatment, and chemical, food, and automotive production. DCS are integrated as a control
architecture containing a supervisory level of control overseeing multiple, integrated sub-systems that are
responsible for controlling the details of a localized process. Product and process control are usually
achieved by deploying feed back or feed forward control loops whereby key product and/or process
conditions are automatically maintained around a desired set point. To accomplish the desired product
and/or process tolerance around a specified set point, specific PLCs are employed in the field and
proportional, integral, and/or derivative settings on the PLC are tuned to provide the desired tolerance as
well as the rate of self-correction during process upsets. DCS are used extensively in process-based
industries.
PLCs are computer-based solid-state devices that control industrial equipment and processes. While
PLCs are control system components used throughout SCADA and DCS systems, they are often the
primary components in smaller control system configurations used to provide operational control of
discrete processes such as automobile assembly lines and power plant soot blower controls. PLCs are
used extensively in almost all industrial processes.
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The process-based manufacturing industries typically utilize two main processes [1]:
Continuous Manufacturing Processes. These processes run continuously, often with transitions to
make different grades of a product. Typical continuous manufacturing processes include fuel or
steam flow in a power plant, petroleum in a refinery, and distillation in a chemical plant.
Batch Manufacturing Processes. These processes have distinct processing steps, conducted on a
quantity of material. There is a distinct start and end step to a batch process with the possibility of
brief steady state operations during intermediate steps. Typical batch manufacturing processes
include food manufacturing.
The discrete-based manufacturing industries typically conduct a series of steps on a single device to
create the end product. Electronic and mechanical parts assembly and parts machining are typical
examples of this type of industry.
Both process-based and discrete-based industries utilize the same types of control systems, sensors, and
networks. Some facilities are a hybrid of discrete and process-based manufacturing.
While control systems used in distribution and manufacturing industries are very similar in operation,
they are different in some aspects. One of the primary differences is that DCS or PLC-controlled sub-
systems are usually located within a more confined factory or plant-centric area, when compared to
geographically dispersed SCADA field sites. DCS and PLC communications are usually performed using
local area network (LAN) technologies that are typically more reliable and high speed compared to the
long-distance communication systems used by SCADA systems. In fact, SCADA systems are
specifically designed to handle long-distance communication challenges such as delays and data loss
posed by the various communication media used. DCS and PLC systems usually employ greater degrees
of closed loop control than SCADA systems because the control of industrial processes is typically more
complicated than the supervisory control of distribution processes. These differences can be considered
subtle for the scope of this document, which focuses on the integration of IT security into these systems.
Throughout the remainder of this document, SCADA systems, DCS and PLC systems will be referred to
as ICS unless a specific reference is made to one (e.g., field device used in a SCADA system).
2.2 ICS Operation
The basic operation of an ICS is shown in Figure 2-1 [2]. Key components include the following:
Control Loop. A control loop consists of sensors for measurement, controller hardware such as
PLCs, actuators such as control valves, breakers, switches and motors, and the communication of
variables. Controlled variables are transmitted to the controller from the sensors. The controller
interprets the signals and generates corresponding manipulated variables, based on set points, which it
transmits to the actuators. Process changes from disturbances result in new sensor signals, identifying
the state of the process, to again be transmitted to the controller.
Human-Machine Interface (HMI). Operators and engineers use HMIs to monitor and configure set
points, control algorithms, and adjust and establish parameters in the controller. The HMI also
displays process status information and historical information.
Remote Diagnostics and Maintenance Utilities. Diagnostics and maintenance utilities are used to
prevent, identify and recover from abnormal operation or failures.
2-2

A typical ICS contains a proliferation of control loops, HMIs, and remote diagnostics and maintenance
tools built using an array of network protocols on layered network architectures. Sometimes these control
loops are nested and/or cascading –whereby the set point for one loop is based on the process variable
determined by another loop. Supervisory-level loops and lower-level loops operate continuously over the
duration of a process with cycle times ranging on the order of milliseconds to minutes.
Figure 2-1. ICS Operation
2.3 Key ICS Components
To support subsequent discussions, this section defines key ICS components that are used in control and
networking. Some of these components can be described generically for use in SCADA systems, DCS
and PLCs, while others are unique to one. The Glossary of Terms in Appendix B contains a more
detailed listing of control and networking components. Additionally, Figure 2-5 and Figure 2-6 in
Section 2.4 show SCADA implementation examples, Figure 2-7 in Section 2.5 shows a DCS
implementation example and Figure 2-8 in Section 2.6 shows a PLC system implementation example that
incorporates these components.
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2.3.1 Control Components
The following is a list of the major control components of an ICS:
Control Server. The control server hosts the DCS or PLC supervisory control software that
communicates with lower-level control devices. The control server accesses subordinate control
modules over an ICS network.
SCADA Server or Master Terminal Unit (MTU). The SCADA Server is the device that acts as the
master in a SCADA system. Remote terminal units and PLC devices (as described below) located at
remote field sites usually act as slaves.
Remote Terminal Unit (RTU). The RTU, also called a remote telemetry unit, is a special purpose
data acquisition and control unit designed to support SCADA remote stations. RTUs are field devices
often equipped with wireless radio interfaces to support remote situations where wire-based
communications are unavailable. Sometimes PLCs are implemented as field devices to serve as
RTUs; in this case, the PLC is often referred to as an RTU.
Programmable Logic Controller (PLC). The PLC is a small industrial computer originally
designed to perform the logic functions executed by electrical hardware (relays, switches, and
mechanical timer/counters). PLCs have evolved into controllers with the capability of controlling
complex processes, and they are used substantially in SCADA systems and DCS. Other controllers
used at the field level are process controllers and RTUs; they provide the same control as PLCs but
are designed for specific control applications. In SCADA environments, PLCs are often used as field
devices because they are more economical, versatile, flexible, and configurable than special-purpose
RTUs.
Intelligent Electronic Devices (IED). An IED is a “smart” sensor/actuator containing the
intelligence required to acquire data, communicate to other devices, and perform local processing and
control. An IED could combine an analog input sensor, analog output, low-level control capabilities,
a communication system, and program memory in one device. The use of IEDs in SCADA and DCS
systems allows for automatic control at the local level.
Human-Machine Interface (HMI). The HMI is software and hardware that allows human operators
to monitor the state of a process under control, modify control settings to change the control
objective, and manually override automatic control operations in the event of an emergency. The
HMI also allows a control engineer or operator to configure set points or control algorithms and
parameters in the controller. The HMI also displays process status information, historical
information, reports, and other information to operators, administrators, managers, business partners,
and other authorized users. The location, platform, and interface may vary a great deal. For example,
an HMI could be a dedicated platform in the control center, a laptop on a wireless LAN, or a browser
on any system connected to the Internet.
Data Historian. The data historian is a centralized database for logging all process information
within an ICS. Information stored in this database can be accessed to support various analyses, from
statistical process control to enterprise level planning.
Input/Output (IO) Server. The IO server is a control component responsible for collecting,
buffering and providing access to process information from control sub-components such as PLCs,
RTUs and IEDs. An IO server can reside on the control server or on a separate computer platform.
IO servers are also used for interfacing third-party control components, such as an HMI and a control
server.
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2.3.2 Network Components
There are different network characteristics for each layer within a control system hierarchy. Network
topologies across different ICS implementations vary with modern systems using Internet-based IT and
enterprise integration strategies. Control networks have merged with corporate networks to allow control
engineers to monitor and control systems from outside of the control system network. The connection
may also allow enterprise-level decision-makers to obtain access to process data. The following is a list of
the major components of an ICS network, regardless of the network topologies in use:
Fieldbus Network. The fieldbus network links sensors and other devices to a PLC or other
controller. Use of fieldbus technologies eliminates the need for point-to-point wiring between the
controller and each device. The devices communicate with the fieldbus controller using a variety of
protocols. The messages sent between the sensors and the controller uniquely identify each of the
sensors.
Control Network. The control network connects the supervisory control level to lower-level control
modules.
Communications Routers. A router is a communications device that transfers messages between
two networks. Common uses for routers include connecting a LAN to a WAN, and connecting
MTUs and RTUs to a long-distance network medium for SCADA communication.
Firewall. A firewall protects devices on a network by monitoring and controlling communication
packets using predefined filtering policies. Firewalls are also useful in managing ICS network
segregation strategies.
Modems. A modem is a device used to convert between serial digital data and a signal suitable for
transmission over a telephone line to allow devices to communicate. Modems are often used in
SCADA systems to enable long-distance serial communications between MTUs and remote field
devices. They are also used in SCADA systems, DCS and PLCs for gaining remote access for
operational and maintenance functions such as entering commands or modifying parameters, and
diagnostic purposes.
Remote Access Points. Remote access points are distinct devices, areas and locations of a control
network for remotely configuring control systems and accessing process data. Examples include
using a personal digital assistant (PDA) to access data over a LAN through a wireless access point,
and using a laptop and modem connection to remotely access an ICS system.
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2.4 SCADA Systems
SCADA systems are used to control dispersed assets where centralized data acquisition is as important as
control [3] [4]. These systems are used in distribution systems such as water distribution and wastewater
collection systems, oil and natural gas pipelines, electrical utility transmission and distribution systems,
and rail and other public transportation systems. SCADA systems integrate data acquisition systems with
data transmission systems and HMI software to provide a centralized monitoring and control system for
numerous process inputs and outputs. SCADA systems are designed to collect field information, transfer
it to a central computer facility, and display the information to the operator graphically or textually,
thereby allowing the operator to monitor or control an entire system from a central location in real time.
Based on the sophistication and setup of the individual system, control of any individual system,
operation, or task can be automatic, or it can be performed by operator commands.
SCADA systems consist of both hardware and software. Typical hardware includes an MTU placed at a
control center, communications equipment (e.g., radio, telephone line, cable, or satellite), and one or more
geographically distributed field sites consisting of either an RTU or a PLC, which controls actuators
and/or monitors sensors. The MTU stores and processes the information from RTU inputs and outputs,
while the RTU or PLC controls the local process. The communications hardware allows the transfer of
information and data back and forth between the MTU and the RTUs or PLCs. The software is
programmed to tell the system what and when to monitor, what parameter ranges are acceptable, and what
response to initiate when parameters change outside acceptable values. An IED, such as a protective
relay, may communicate directly to the SCADA Server, or a local RTU may poll the IEDs to collect the
data and pass it to the SCADA Server. IEDs provide a direct interface to control and monitor equipment
and sensors. IEDs may be directly polled and controlled by the SCADA Server and in most cases have
local programming that allows for the IED to act without direct instructions from the SCADA control
center. SCADA systems are usually designed to be fault-tolerant systems with significant redundancy
built into the system architecture.
Figure 2-2 shows the components and general configuration of a SCADA system. The control center
houses a SCADA Server (MTU) and the communications routers. Other control center components
include the HMI, engineering workstations, and the data historian, which are all connected by a LAN.
The control center collects and logs information gathered by the field sites, displays information to the
HMI, and may generate actions based upon detected events. The control center is also responsible for
centralized alarming, trend analyses, and reporting. The field site performs local control of actuators and
monitors sensors. Field sites are often equipped with a remote access capability to allow field operators
to perform remote diagnostics and repairs usually over a separate dial up modem or WAN connection.
Standard and proprietary communication protocols running over serial communications are used to
transport information between the control center and field sites using telemetry techniques such as
telephone line, cable, fiber, and radio frequency such as broadcast, microwave and satellite.
MTU-RTU communication architectures vary among implementations. The various architectures used,
including point-to-point, series, series-star, and multi-drop [5], are shown in Figure 2-3. Point-to-point is
functionally the simplest type; however, it is expensive because of the individual channels needed for
each connection. In a series configuration, the number of channels used is reduced; however, channel
sharing has an impact on the efficiency and complexity of SCADA operations. Similarly, the series-star
and multi-drop configurations’ use of one channel per device results in decreased efficiency and increased
system complexity.
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Figure 2-2. SCADA System General Layout
The four basic architectures shown in Figure 2-3 can be further augmented using dedicated
communication devices to manage communication exchange as well as message switching and buffering.
Large SCADA systems, containing hundreds of RTUs, often employ sub-MTUs to alleviate the burden
on the primary MTU. This type of topology is shown in Figure 2-4.
Figure 2-5 shows an example of a SCADA system implementation. This particular SCADA system
consists of a primary control center and three field sites. A second backup control center provides
redundancy in the event of a primary control center malfunction. Point-to-point connections are used for
all control center to field site communications, with two connections using radio telemetry. The third
field site is local to the control center and uses the wide area network (WAN) for communications. A
regional control center resides above the primary control center for a higher level of supervisory control.
The corporate network has access to all control centers through the WAN, and field sites can be accessed
remotely for troubleshooting and maintenance operations. The primary control center polls field devices
for data at defined intervals (e.g., 5 seconds, 60 seconds) and can send new set points to a field device as
required. In addition to polling and issuing high-level commands, the SCADA server also watches for
priority interrupts coming from field site alarm systems.
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Figure 2-3. Basic SCADA Communication Topologies
Figure 2-4. Large SCADA Communication Topology
2-8

Figure 2-5. SCADA System Implementation Example (Distribution Monitoring and Control)
Figure 2-6 shows an example implementation for rail monitoring and control. This example includes a
rail control center that houses the SCADA system and three sections of a rail system. The SCADA
system polls the rail sections for information such as the status of the trains, signal systems, traction
electrification systems, and ticket vending machines. This information is also fed to operator consoles at
the HMI station within the rail control center. The SCADA system also monitors operator inputs at the
rail control center and disperses high-level operator commands to the rail section components. In
addition, the SCADA system monitors conditions at the individual rail sections and issues commands
based on these conditions (e.g., shut down a train to prevent it from entering an area that has been
determined to be flooded or occupied by another train based on condition monitoring).
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Figure 2-6. SCADA System Implementation Example (Rail Monitoring and Control)
2.5 Distributed Control Systems
DCS are used to control production systems within the same geographic location for industries such as oil
refineries, water and wastewater treatment, electric power generation plants, chemical manufacturing
plants, and pharmaceutical processing facilities. These systems are usually process control or discrete
part control systems. A DCS uses a centralized supervisory control loop to mediate a group of localized
controllers that share the overall tasks of carrying out an entire production process [6]. By modularizing
the production system, a DCS reduces the impact of a single fault on the overall system. In many modern
systems, the DCS is interfaced with the corporate network to give business operations a view of
production.
An example implementation showing the components and general configuration of a DCS is depicted in
Figure 2-7. This DCS encompasses an entire facility from the bottom-level production processes up to
the corporate or enterprise layer. In this example, a supervisory controller (control server) communicates
to its subordinates via a control network. The supervisor sends set points to and requests data from the
distributed field controllers. The distributed controllers control their process actuators based on control
server commands and sensor feedback from process sensors.
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Figure 2-7 gives examples of low-level controllers found on a DCS system. The field control devices
shown include a PLC, a process controller, a single loop controller, and a machine controller. The single
loop controller interfaces sensors and actuators using point-to-point wiring, while the other three field
devices incorporate fieldbus networks to interface with process sensors and actuators. Fieldbus networks
eliminate the need for point-to-point wiring between a controller and individual field sensors and
actuators. Additionally, a fieldbus allows greater functionality beyond control, including field device
diagnostics, and can accomplish control algorithms within the fieldbus, thereby avoiding signal routing
back to the PLC for every control operation. Standard industrial communication protocols designed by
industry groups such as Modbus and Fieldbus [7] are often used on control networks and fieldbus
networks.
In addition to the supervisory-level and field-level control loops, intermediate levels of control may also
exist. For example, in the case of a DCS controlling a discrete part manufacturing facility, there could be
an intermediate level supervisor for each cell within the plant. This supervisor would encompass a
manufacturing cell containing a machine controller that processes a part and a robot controller that
handles raw stock and final products. There could be several of these cells that manage field-level
controllers under the main DCS supervisory control loop.
Figure 2-7. DCS Implementation Example
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2.6 Programmable Logic Controllers
PLCs are used in both SCADA and DCS systems as the control components of an overall hierarchical
system to provide local management of processes through feedback control as described in the sections
above. In the case of SCADA systems, they provide the same functionality of RTUs. When used in
DCS, PLCs are implemented as local controllers within a supervisory control scheme. PLCs are also
implemented as the primary components in smaller control system configurations. PLCs have a user-
programmable memory for storing instructions for the purpose of implementing specific functions such as
I/O control, logic, timing, counting, three mode proportional-integral-derivative (PID) control,
communication, arithmetic, and data and file processing. Figure 2-8 shows control of a manufacturing
process being performed by a PLC over a fieldbus network. The PLC is accessible via a programming
interface located on an engineering workstation, and data is stored in a data historian, all connected on a
LAN.
Figure 2-8. PLC Control System Implementation Example
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2-13
2.7 Industrial Sectors and Their Interdependencies
Both the electrical power transmission and distribution grid industries use geographically distributed
SCADA control technology to operate highly interconnected and dynamic systems consisting of
thousands of public and private utilities and rural cooperatives for supplying electricity to end users.
SCADA systems monitor and control electricity distribution by collecting data from and issuing
commands to geographically remote field control stations from a centralized location. SCADA systems
are also used to monitor and control water, oil and natural gas distribution, including pipelines, ships,
trucks, and rail systems, as well as wastewater collection systems.
SCADA systems and DCS are often networked together. This is the case for electric power control
centers and electric power generation facilities. Although the electric power generation facility operation
is controlled by a DCS, the DCS must communicate with the SCADA system to coordinate production
output with transmission and distribution demands.
The U.S. critical infrastructure is often referred to as a “system of systems” because of the
interdependencies that exist between its various industrial sectors as well as interconnections between
business partners [8] [9]. Critical infrastructures are highly interconnected and mutually dependent in
complex ways, both physically and through a host of information and communications technologies. An
incident in one infrastructure can directly and indirectly affect other infrastructures through cascading and
escalating failures.
Electric power is often thought to be one of the most prevalent sources of disruptions of interdependent
critical infrastructures. As an example, a cascading failure can be initiated by a disruption of the
microwave communications network used for an electric power transmission SCADA system. The lack
of monitoring and control capabilities could cause a large generating unit to be taken offline, an event that
would lead to loss of power at a transmission substation. This loss could cause a major imbalance,
triggering a cascading failure across the power grid. This could result in large area blackouts that could
potentially affect oil and natural gas production, refinery operations, water treatment systems, wastewater
collection systems, and pipeline transport systems that rely on the grid for electric power.

3. ICS Characteristics, Threats and Vulnerabilities
Most ICS in use today were developed years ago, long before public and private networks, desktop
computing, or the Internet were a common part of business operations. These systems were designed to
meet performance, reliability, safety, and flexibility requirements. In most cases they were physically
isolated from outside networks and based on proprietary hardware, software, and communication
protocols that included basic error detection and correction capabilities, but lacked the secure
communication capabilities required in today’s interconnected systems. While there was concern for
Reliability, Maintainability, and Availability (RMA) when addressing statistical performance and failure,
the need for cyber security measures within these systems was not anticipated. At the time, security for
ICS meant physically securing access to the network and the consoles that controlled the systems.
ICS development paralleled the evolution of microprocessor, personal computer, and networking
technologies during the 1980’s and 1990’s, and Internet-based technologies started making their way into
ICS designs in the late 1990’s. These changes to ICS exposed them to new types of threats and
significantly increased the likelihood that ICS could be compromised. This section describes the unique
security characteristics of ICS, the vulnerabilities in ICS implementations, and the threats and incidents
that ICS may face. Section 3.7 presents several examples of actual ICS cyber security incidents.
3.1 Comparing ICS and IT Systems
Initially, ICS had little resemblance to IT systems in that ICS were isolated systems running proprietary
control protocols using specialized hardware and software. Widely available, low-cost Internet Protocol
(IP) devices are now replacing proprietary solutions, which increases the possibility of cyber security
vulnerabilities and incidents. As ICS are adopting IT solutions to promote corporate connectivity and
remote access capabilities, and are being designed and implemented using industry standard computers,
operating systems (OS) and network protocols, they are starting to resemble IT systems. This integration
supports new IT capabilities, but it provides significantly less isolation for ICS from the outside world
than predecessor systems, creating a greater need to secure these systems. While security solutions have
been designed to deal with these security issues in typical IT systems, special precautions must be taken
when introducing these same solutions to ICS environments. In some cases, new security solutions are
needed that are tailored to the ICS environment.
ICS have many characteristics that differ from traditional IT systems, including different risks and
priorities. Some of these include significant risk to the health and safety of human lives, serious damage
to the environment, and financial issues such as production losses, and negative impact to a nation’s
economy. ICS have different performance and reliability requirements and use operating systems and
applications that may be considered unconventional to typical IT support personnel. Furthermore, the
goals of safety and efficiency can sometimes conflict with security in the design and operation of control
systems (e.g., requiring password authentication and authorization should not hamper or interfere with
emergency actions for ICS.) The following lists some special considerations when considering security
for ICS:
Performance Requirements. ICS are generally time-critical, with the criterion for acceptable levels
of delay and jitter dictated by the individual installation. Some systems require deterministic
responses. High throughput is typically not essential to ICS. In contrast, IT systems typically require
high throughput, and they can typically withstand some level of delay and jitter
Availability Requirements. Many ICS processes are continuous in nature. Unexpected outages of
systems that control industrial processes are not acceptable. Outages often must be planned and
scheduled days/weeks in advance. Exhaustive pre-deployment testing is essential to ensure high
3-1

availability for the ICS. In addition to unexpected outages, many control systems cannot be easily
stopped and started without affecting production. In some cases, the products being produced or
equipment being used is more important than the information being relayed. Therefore, the use of
typical IT strategies such as rebooting a component, are usually not acceptable solutions due to the
adverse impact on the requirements for high availability, reliability and maintainability of the ICS.
Some ICS employ redundant components, often running in parallel, to provide continuity when
primary components are unavailable.
Risk Management Requirements. In a typical IT system, data confidentiality and integrity are
typically the primary concerns. For an ICS, human safety and fault tolerance to prevent loss of life or
endangerment of public health or confidence, regulatory compliance, loss of equipment, loss of
intellectual property, or lost or damaged products are the primary concerns. The personnel
responsible for operating, securing, and maintaining ICS must understand the important link between
safety and security.
Architecture Security Focus. In a typical IT system, the primary focus of security is protecting the
operation of IT assets, whether centralized or distributed, and the information stored on or transmitted
among these assets. In some architectures, information stored and processed centrally is more critical
and is afforded more protection. For ICS, edge clients (e.g., PLC, operator station, DCS controller)
need to be carefully protected because they are directly responsible for controlling the end processes.
The protection of the central server is still very important in an ICS, because the central server could
possibly adversely impact every edge device.
Physical Interaction. In a typical IT system, there is not physical interaction with the environment.
ICS can have very complex interactions with physical processes and consequences in the ICS domain
that can manifest in physical events. All security functions integrated into the ICS must be tested
(e.g., off-line on a comparable ICS) to prove that they do not compromise normal ICS functionality.
Time-Critical Responses. In a typical IT system, access control can be implemented without
significant regard for data flow. For some ICS, automated response time or system response to
human interaction is very critical. For example, requiring password authentication and authorization
on an HMI must not hamper or interfere with emergency actions for ICS. Information flow must not
be interrupted or compromised. Access to these systems should be restricted by rigorous physical
security controls.
System Operation. ICS operating systems (OS) and applications may not tolerate typical IT security
practices. Legacy systems are especially vulnerable to resource unavailability and timing disruptions.
Control networks are often more complex and require a different level of expertise (e.g., control
networks are typically managed by control engineers, not IT personnel). Software and hardware are
more difficult to upgrade in an operational control system network. Many systems may not have
desired features including encryption capabilities, error logging, and password protection.
Resource Constraints. ICS and their real time OSs are often resource-constrained systems that
usually do not include typical IT security capabilities. There may not be computing resources
available on ICS components to retrofit these systems with current security capabilities. Additionally,
in some instances, third-party security solutions are not allowed due to ICS vendor license and service
agreements, and loss of service support can occur if third party applications are installed without
vendor acknowledgement or approval.
Communications. Communication protocols and media used by ICS environments for field device
control and intra-processor communication are typically different from the generic IT environment,
and may be proprietary.
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Change Management. Change management is paramount to maintaining the integrity of both IT and
control systems. Unpatched software represents one of the greatest vulnerabilities to a system.
Software updates on IT systems, including security patches, are typically applied in a timely fashion
based on appropriate security policy and procedures. In addition, these procedures are often
automated using server-based tools. Software updates on ICS cannot always be implemented on a
timely basis because these updates need to be thoroughly tested by the vendor of the industrial control
application and the end user of the application before being implemented and ICS outages often must
be planned and scheduled days/weeks in advance. The ICS may also require revalidation as part of
the update process. Another issue is that many ICS utilize older versions of operating systems that
are no longer supported by the vendor. Consequently, available patches may not be applicable.
Change management is also applicable to hardware and firmware. The change management process,
when applied to ICS, requires careful assessment by ICS experts (e.g., control engineers) working in
conjunction with security and IT personnel.
Managed Support. Typical IT systems allow for diversified support styles, perhaps supporting
disparate but interconnected technology architectures. For ICS, service support is usually via a single
vendor, which may not have a diversified and interoperable support solution from another vendor.
Component Lifetime. Typical IT components have a lifetime on the order of 3 to 5 years, with
brevity due to the quick evolution of technology. For ICS where technology has been developed in
many cases for very specific use and implementation, the lifetime of the deployed technology is often
in the order of 15 to 20 years and sometimes longer.
Access to Components. Typical IT components are usually local and easy to access, while ICS
components can be isolated, remote, and require extensive physical effort to gain access to them.
Table 3-1 summarizes some of the typical differences between IT systems and ICS.
Table 3-1. Summary of IT System and ICS Differences
Category Information Technology System Industrial Control System
Performance
Requirements
Non-real-time
Response must be consistent
High throughput is demanded
High delay and jitter may be acceptable
Real-time
Response is time-critical
Modest throughput is acceptable
High delay and/or jitter is not acceptable
Availability
Requirements
Responses such as rebooting are acceptable
Availability deficiencies can often be
tolerated, depending on the system’s
operational requirements
Responses such as rebooting may not be
acceptable because of process availability
requirements
Availability requirements may necessitate
redundant systems
Outages must be planned and scheduled
days/weeks in advance
High availability requires exhaustive pre-
deployment testing
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Category Information Technology System Industrial Control System
Risk
Management
Requirements
Data confidentiality and integrity is
paramount
Fault tolerance is less important –
momentary downtime is not a major risk
Major risk impact is delay of business
operations
Human safety is paramount, followed by
protection of the process
Fault tolerance is essential, even momentary
downtime may not be acceptable
Major risk impacts are regulatory non-
compliance, environmental impacts, loss of
life, equipment, or production
Architecture
Security Focus
Primary focus is protecting the IT assets, and
the information stored on or transmitted
among these assets.
Central server may require more protection
Primary goal is to protect edge clients (e.g.,
field devices such as process controllers)
Protection of central server is also important
Unintended
Consequences
Security solutions are designed around
typical IT systems
Security tools must be tested (e.g., off-line on
a comparable ICS) to ensure that they do not
compromise normal ICS operation
Time-Critical
Interaction
Less critical emergency interaction
Tightly restricted access control can be
implemented to the degree necessary for
security
Response to human and other emergency
interaction is critical
Access to ICS should be strictly controlled,
but should not hamper or interfere with
human-machine interaction
System
Operation
Systems are designed for use with typical
operating systems
Upgrades are straightforward with the
availability of automated deployment tools
Differing and possibly proprietary operating
systems, often without security capabilities
built in
Software changes must be carefully made,
usually by software vendors, because of the
specialized control algorithms and perhaps
modified hardware and software involved
Resource
Constraints
Systems are specified with enough
resources to support the addition of third-
party applications such as security solutions
Systems are designed to support the
intended industrial process and may not have
enough memory and computing resources to
support the addition of security capabilities
Communications Standard communications protocols
Primarily wired networks with some localized
wireless capabilities
Typical IT networking practices
Many proprietary and standard
communication protocols
Several types of communications media used
including dedicated wire and wireless (radio
and satellite)
Networks are complex and sometimes require
the expertise of control engineers
Change
Management
Software changes are applied in a timely
fashion in the presence of good security
policy and procedures. The procedures are
often automated.
Software changes must be thoroughly tested
and deployed incrementally throughout a
system to ensure that the integrity of the
control system is maintained. ICS outages
often must be planned and scheduled
days/weeks in advance. ICS may use OSs
that are no longer supported
Managed
Support
Allow for diversified support styles Service support is usually via a single vendor
Component
Lifetime
Lifetime on the order of 3-5 years Lifetime on the order of 15-20 years
Access to
Components
Components are usually local and easy to
access
Components can be isolated, remote, and
require extensive physical effort to gain
access to them
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Available computing resources for ICS (including central processing unit [CPU] time and memory) tend
to be very limited because these systems were designed to maximize control system resources, with little
to no extra capacity for third-party cyber security solutions. Additionally, in some instances, third-party
security solutions are not allowed due to vendor license and service agreements, and loss of service
support can occur if third party applications are installed. Another important consideration is that IT
cyber security and control systems expertise is typically not found within the same group of personnel.
In summary, the operational and risk differences between ICS and IT systems create the need for
increased sophistication in applying cyber security and operational strategies. A cross-functional team of
control engineers, control system operators and IT security professionals needs to work closely to
understand the possible implications of the installation, operation, and maintenance of security solutions
in conjunction with control system operation. IT professionals working with ICS need to understand the
reliability impacts of information security technologies before deployment. Some of the OSs and
applications running on ICS may not operate correctly with commercial-off-the-shelf (COTS) IT cyber
security solutions because of specialized ICS environment architectures.
3.2 Threats
Threats to control systems can come from numerous sources, including adversarial sources such as hostile
governments, terrorist groups, industrial spies, disgruntled employees, malicious intruders, and natural
sources such as from system complexities, human errors and accidents, equipment failures and natural
disasters. To protect against adversarial threats (as well as known natural threats), it is necessary to create
a defense-in-depth strategy for the ICS. Table 3-2 lists possible threats to ICS. Please note this list is in
alphabetical order and not by greatest threat.
Table 3-2. Adversarial Threats to ICS
Threat Agent Description
Attackers Attackers break into networks for the thrill of the challenge or for bragging rights in the
attacker community. While remote cracking once required a fair amount of skill or computer
knowledge, attackers can now download attack scripts and protocols from the Internet and
launch them against victim sites. Thus, while attack tools have become more sophisticated,
they have also become easier to use. Many attackers do not have the requisite expertise to
threaten difficult targets such as critical U.S. networks. Nevertheless, the worldwide
population of attackers poses a relatively high threat of an isolated or brief disruption
causing serious damage.
Bot-network
operators
Bot-network operators are attackers; however, instead of breaking into systems for the
challenge or bragging rights, they take over multiple systems to coordinate attacks and to
distribute phishing schemes, spam, and malware attacks. The services of compromised
systems and networks are sometimes made available on underground markets (e.g.,
purchasing a denial of service attack or the use of servers to relay spam or phishing
attacks).
Criminal groups Criminal groups seek to attack systems for monetary gain. Specifically, organized crime
groups are using spam, phishing, and spyware/malware to commit identity theft and online
fraud. International corporate spies and organized crime organizations also pose a threat to
the U.S. through their ability to conduct industrial espionage and large-scale monetary theft
and to hire or develop attacker talent. Some criminal groups may try to extort money from
an organization by threatening a cyber attack.
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Threat Agent Description
Foreign intelligence
services
Foreign intelligence services use cyber tools as part of their information gathering and
espionage activities. In addition, several nations are aggressively working to develop
information warfare doctrines, programs, and capabilities. Such capabilities enable a single
entity to have a significant and serious impact by disrupting the supply, communications,
and economic infrastructures that support military power – impacts that could affect the daily
lives of U.S. citizens.
Insiders The disgruntled insider is a principal source of computer crime. Insiders may not need a
great deal of knowledge about computer intrusions because their knowledge of a target
system often allows them to gain unrestricted access to cause damage to the system or to
steal system data. The insider threat also includes outsourcing vendors as well as
employees who accidentally introduce malware into systems. Insiders may be employees,
contractors, or business partners.
Inadequate policies, procedures, and testing can, and have led to ICS impacts. Impacts
have ranged from trivial to significant damage to the ICS and field devices. Unintentional
impacts from insiders are some of the highest probability occurrences.
Phishers Phishers are individuals or small groups that execute phishing schemes in an attempt to
steal identities or information for monetary gain. Phishers may also use spam and
spyware/malware to accomplish their objectives.
Spammers Spammers are individuals or organizations that distribute unsolicited e-mail with hidden or
false information to sell products, conduct phishing schemes, distribute spyware/malware, or
attack organizations (e.g., DoS).
Spyware/malware
authors
Individuals or organizations with malicious intent carry out attacks against users by
producing and distributing spyware and malware. Several destructive computer viruses and
worms have harmed files and hard drives, including the Melissa Macro Virus, the
Explore.Zip worm, the CIH (Chernobyl) Virus, Nimda, Code Red, Slammer, and Blaster.
Terrorists Terrorists seek to destroy, incapacitate, or exploit critical infrastructures to threaten national
security, cause mass casualties, weaken the U.S. economy, and damage public morale and
confidence. Terrorists may use phishing schemes or spyware/malware to generate funds or
gather sensitive information. Terrorists may attack one target to divert attention or
resources from other targets.
Industrial spies Industrial espionage seeks to acquire intellectual property and know-how by clandestine
methods
Source: Government Accountability Office (GAO), Department of Homeland Security’s (DHS’s) Role in Critical Infrastructure
Protection (CIP) Cybersecurity, GAO-05-434 (Washington, D.C.: May, 2005).
3.3 Potential ICS Vulnerabilities
This section lists vulnerabilities that may be found in typical ICS. The order of these vulnerabilities does
not necessarily reflect any priority in terms of likelihood of occurrence or severity of impact. The
vulnerabilities are grouped into Policy and Procedure, Platform, and Network categories to assist in
determining optimal mitigation strategies. Any given ICS will usually exhibit a subset of these
vulnerabilities, but may also contain additional vulnerabilities unique to the particular ICS
implementation that do not appear in this listing. Specific information on ICS vulnerabilities can be
researched at the United States Computer Emergency Readiness Team (US-CERT) Control Systems Web
site.2
When studying possible security vulnerabilities, it is easy to become preoccupied with trying to address
issues that are technically interesting, but are ultimately of low impact. As addressed in Appendix E,
2
The US-CERT Control Systems Web site is located at http://www.us-cert.gov/control_systems/.
3-6

FIPS 199 establishes security categories for both information and information systems based on the
potential impact on an organization should certain events occur which jeopardize the information and
information systems needed by the organization to accomplish its assigned mission, protect its assets,
fulfill its legal responsibilities, maintain its day-to-day functions, and protect individuals.
A method for assessing and rating the risk of a possible vulnerability at a specific facility is needed. The
risk is a function of the likelihood (probability) that a defined threat agent (adversary) can exploit a
specific vulnerability and create an impact (consequence). The risk induced by any given vulnerability is
influenced by a number of related indicators, including:
Network and computer architecture and conditions
Installed countermeasures
Technical difficulty of the attack
Probability of detection (e.g., amount of time the adversary can remain in contact with the target
system/network without detection)
Consequences of the incident
Cost of the incident.
This assessment of risk is addressed in further detail in Sections 4 through 6.
3.3.1 Policy and Procedure Vulnerabilities
Vulnerabilities are often introduced into ICS because of incomplete, inappropriate, or nonexistent security
documentation, including policy and implementation guides (procedures). Security documentation, along
with management support, is the cornerstone of any security program. Corporate security policy can
reduce vulnerabilities by mandating conduct such as password usage and maintenance or requirements for
connecting modems to ICS. Table 3-3 describes potential policy and procedure vulnerabilities for ICS.
Table 3-3. Policy and Procedure Vulnerabilities
Vulnerability Description
Inadequate security policy for the
ICS
Vulnerabilities are often introduced into ICS due to inadequate policies or
the lack of policies specifically for control system security.
No formal ICS security training and
awareness program
A documented formal security training and awareness program is designed
to keep staff up to date on organizational security policies and procedures
as well as industry cyber security standards and recommended practices.
Without training on specific ICS policies and procedures, staff cannot be
expected to maintain a secure ICS environment.
Inadequate security architecture
and design
Control engineers have historically had minimal training in security and until
relatively recently vendors have not included security features in their
products
No specific or documented security
procedures were developed from
the security policy for the ICS
Specific security procedures should be developed and employees trained
for the ICS. They are the roots of a sound security program.
Absent or deficient ICS equipment
implementation guidelines
Equipment implementation guidelines should be kept up to date and readily
available. These guidelines are an integral part of security procedures in
the event of an ICS malfunction.
Lack of administrative mechanisms
for security enforcement
Staff responsible for enforcing security should be held accountable for
administering documented security policies and procedures.
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Few or no security audits on the
ICS
Independent security audits should review and examine a system’s records
and activities to determine the adequacy of system controls and ensure
compliance with established ICS security policy and procedures. Audits
should also be used to detect breaches in ICS security services and
recommend changes, which may include making existing security controls
more robust and/or adding new security controls.
No ICS specific continuity of
operations or disaster recovery
plan (DRP)
A DRP should be prepared, tested and available in the event of a major
hardware or software failure or destruction of facilities. Lack of a specific
DRP for the ICS could lead to extended downtimes and production loss.
Lack of ICS specific configuration
change management
A process for controlling modifications to hardware, firmware, software, and
documentation should be implemented to ensure an ICS is protected
against inadequate or improper modifications before, during, and after
system implementation. A lack of configuration change management
procedures can lead to security oversights, exposures, and risks.
3.3.2 Platform Vulnerabilities
Vulnerabilities in ICS can occur due to flaws, misconfigurations, or poor maintenance of their platforms,
including hardware, operating systems, and ICS applications. These vulnerabilities can be mitigated
through various security controls, such as OS and application patching, physical access control, and
security software (e.g., antivirus software). The tables in this section describe potential platform
vulnerabilities:
Table 3-4. Platform Configuration Vulnerabilities
Table 3-5. Platform Hardware Vulnerabilities
Table 3-6. Platform Software Vulnerabilities
Table 3-7. Platform Malware Protection Vulnerabilities
Table 3-4. Platform Configuration Vulnerabilities
OS and vendor software patches
may not be developed until
significantly after security
vulnerabilities are found
Because of the complexity of ICS software and possible modifications to the
underlying OS, changes must undergo comprehensive regression testing.
The elapsed time for such testing and subsequent distribution of updated
software provides a long window of vulnerability
OS and application security
patches are not maintained
Out-of-date OSs and applications may contain newly discovered
vulnerabilities that could be exploited. Documented procedures should be
developed for how security patches will be maintained. Security patch
support may not even be available for ICS that use outdated OSs.
OS and application security
patches are implemented without
exhaustive testing
OS and application security patches deployed without testing could
compromise normal operation of the ICS. Documented procedures should
be developed for testing new security patches.
Default configurations are used Using default configurations often leads to insecure and unnecessary open
ports and exploitable services and applications running on hosts.
Critical configurations are not
stored or backed up
Procedures should be available for restoring ICS configuration settings in
the event of accidental or adversary-initiated configuration changes to
maintain system availability and prevent loss of data. Documented
procedures should be developed for maintaining ICS configuration settings.
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Data unprotected on portable
device
If sensitive data (e.g., passwords, dial-up numbers) is stored in the clear on
portable devices such as laptops and PDAs and these devices are lost or
stolen, system security could be compromised. Policy, procedures, and
mechanisms are required for protection.
Lack of adequate password policy Password policies are needed to define when passwords must be used,
how strong they must be, and how they must be maintained. Without a
password policy, systems might not have appropriate password controls,
making unauthorized access to systems more likely. Password policies
should be developed as part of an overall ICS security program taking into
account the capabilities of the ICS and its personnel to handle more
complex passwords.
No password used Passwords should be implemented on ICS components to prevent
unauthorized access. Password-related vulnerabilities include having no
password for:
• System login (if the system has user accounts)
• System power-on (if the system has no user accounts)
• System screen saver (if an ICS component is unattended over
time)
Password authentication should not hamper or interfere with emergency
actions for ICS.
Password disclosure Passwords should be kept confidential to prevent unauthorized access.
Examples of password disclosures include:
• Posting passwords in plain sight, local to a system
• Sharing passwords to individual user accounts with associates
• Communicating passwords to adversaries through social
engineering
• Sending passwords that are not encrypted through unprotected
communications
Password guessing Poorly chosen passwords can easily be guessed by humans or computer
algorithms to gain unauthorized access. Examples include:
• Passwords that are short, simple (e.g., all lower-case letters), or
otherwise do not meet typical strength requirements. Password
strength also depends on the specific ICS capability to handle
more stringent passwords
• Passwords that are left as the default vendor supplied value
• Passwords that are not changed on a specified interval
Inadequate access controls applied Poorly specified access controls can result in giving an ICS user too many
or too few privileges. The following exemplify each case:
• System configured with default access control settings gives an
operator administrative privileges
• System improperly configured results in an operator being unable
to take corrective actions in an emergency situation
Access control policies should be developed as part of an ICS security
program.
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Table 3-5. Platform Hardware Vulnerabilities
Inadequate testing of security
changes
Many ICS facilities, especially smaller facilities, have no test facilities, so
security changes must be implemented using the live operational systems
Inadequate physical protection for
critical systems
Access to the control center, field devices, portable devices, media, and
other ICS components needs to be controlled. Many remote sites are often
not staffed and it may not be feasible to physically monitor them.
Unauthorized personnel have
physical access to equipment
Physical access to ICS equipment should be restricted to only the
necessary personnel, taking into account safety requirements, such as
emergency shutdown or restarts. Improper access to ICS equipment can
lead to any of the following:
• Physical theft of data and hardware
• Physical damage or destruction of data and hardware
• Unauthorized changes to the functional environment (e.g., data
connections, unauthorized use of removable media,
adding/removing resources)
• Disconnection of physical data links
• Undetectable interception of data (keystroke and other input
logging)
Insecure remote access on ICS
components
Modems and other remote access capabilities that enable control engineers
and vendors to gain remote access to systems should be deployed with
security controls to prevent unauthorized individuals from gaining access to
the ICS.
Dual network interface cards (NIC)
to connect networks
Machines with dual NICs connected to different networks could allow
unauthorized access and passing of data from one network to another.
Undocumented assets To properly secure an ICS, there should be an accurate listing of the assets
in the system. An inaccurate representation of the control system and its
components could leave an unauthorized access point or backdoor into the
ICS.
Radio frequency and electro-
magnetic pulse (EMP)
The hardware used for control systems is vulnerable to radio frequency and
electro-magnetic pulses (EMP). The impact can range from temporary
disruption of command and control to permanent damage to circuit boards.
Lack of backup power Without backup power to critical assets, a general loss of power will shut
down the ICS and could create an unsafe situation. Loss of power could
also lead to insecure default settings.
Loss of environmental control Loss of environmental control could lead to processors overheating. Some
processors will shut down to protect themselves; some may continue to
operate but in a minimal capacity, producing intermittent errors; and some
just melt if they overheat.
Lack of redundancy for critical
components
Lack of redundancy in critical components could provide single point of
failure possibilities
Table 3-6. Platform Software Vulnerabilities
Buffer overflow Software used to implement an ICS could be vulnerable to buffer overflows;
adversaries could exploit these to perform various attacks.
Installed security capabilities not
enabled by default
Security capabilities that were installed with the product are useless if they
are not enabled or at least identified as being disabled.
Denial of service (DoS) ICS software could be vulnerable to DoS attacks, resulting in the prevention
of authorized access to a system resource or delaying system operations
and functions.
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Mishandling of undefined, poorly
defined, or “illegal” conditions
Some ICS implementations are vulnerable to packets that are malformed or
contain illegal or otherwise unexpected field values.
OLE for Process Control (OPC)
relies on Remote Procedure Call
(RPC) and Distributed Component
Object Model (DCOM)
Without updated patches, OPC is vulnerable to the known RPC/DCOM
vulnerabilities.
Use of insecure industry-wide ICS
protocols
Distributed Network Protocol (DNP) 3.0, Modbus, Profibus, and other
protocols are common across several industries and protocol information is
freely available. These protocols often have few or no security capabilities
built in.
Use of clear text Many ICS protocols transmit messages in clear text across the transmission
media, making them susceptible to eavesdropping by adversaries.
Unneeded services running Many platforms have a wide variety of processor and network services
defined to operate as a default. Unneeded services are seldom disabled
and could be exploited.
Use of proprietary software that
has been discussed at conferences
and in periodicals
Proprietary software issues are discussed at international IT, ICS and “Black
Hat” conferences and available through technical papers, periodicals and
listservers. Also, ICS maintenance manuals are available from the vendors.
This information can help adversaries create successful attacks against ICS.
Inadequate authentication and
access control for configuration and
programming software
Unauthorized access to configuration and programming software could
provide the ability to corrupt a device.
Intrusion detection/prevention
software not installed
Incidents can result in loss of system availability; the capture, modification,
and deletion of data; and incorrect execution of control commands. IDS/IPS
software may stop or prevent various types of attacks, including DoS
attacks, and also identify attacked internal hosts, such as those infected with
worms. IDS/IPS software must be tested prior to deployment to determine
that it does not compromise normal operation of the ICS.
Logs not maintained Without proper and accurate logs, it might be impossible to determine what
caused a security event to occur.
Incidents are not detected Where logs and other security sensors are installed, they may not be
monitored on a real-time basis and therefore security incidents may not be
rapidly detected and countered.
Table 3-7. Platform Malware Protection Vulnerabilities
Malware protection software not
installed
Malicious software can result in performance degradation, loss of system
availability, and the capture, modification, or deletion of data. Malware
protection software, such as antivirus software, is needed to prevent
systems from being infected by malicious software.
Malware protection software or
definitions not current
Outdated malware protection software and definitions leave the system
open to new malware threats.
Malware protection software
implemented without exhaustive
testing
Malware protection software deployed without testing could impact normal
operation of the ICS.
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3.3.3 Network Vulnerabilities
Vulnerabilities in ICS may occur from flaws, misconfigurations, or poor administration of ICS networks
and their connections with other networks. These vulnerabilities can be eliminated or mitigated through
various security controls, such as defense-in-depth network design, encrypting network communications,
restricting network traffic flows, and providing physical access control for network components.
The tables in this section describe potential platform vulnerabilities:
Table 3-8. Network Configuration Vulnerabilities
Table 3-9. Network Hardware Vulnerabilities
Table 3-10. Network Perimeter Vulnerabilities
Table 3-11. Network Monitoring and Logging Vulnerabilities
Table 3-12. Communication Vulnerabilities
Table 3-13. Wireless Connection Vulnerabilities
Table 3-8. Network Configuration Vulnerabilities
Weak network security architecture The network infrastructure environment within the ICS has often been
developed and modified based on business and operational requirements,
with little consideration for the potential security impacts of the changes.
Over time, security gaps may have been inadvertently introduced within
particular portions of the infrastructure. Without remediation, these gaps
may represent backdoors into the ICS.
Data flow controls not employed Data flow controls, such as access control lists (ACL), are needed to restrict
which systems can directly access network devices. Generally, only
designated network administrators should be able to access such devices
directly. Data flow controls should ensure that other systems cannot directly
access the devices.
Poorly configured security
equipment
Using default configurations often leads to insecure and unnecessary open
ports and exploitable network services running on hosts. Improperly
configured firewall rules and router ACLs can allow unnecessary traffic.
Network device configurations not
stored or backed up
Procedures should be available for restoring network device configuration
settings in the event of accidental or adversary-initiated configuration
changes to maintain system availability and prevent loss of data.
Documented procedures should be developed for maintaining network
device configuration settings.
Passwords are not encrypted in
transit
Passwords transmitted in clear text across transmission media are
susceptible to eavesdropping by adversaries, who could reuse them to gain
unauthorized access to a network device. Such access could allow an
adversary to disrupt ICS operations or to monitor ICS network activity.
Passwords exist indefinitely on
network devices
Passwords should be changed regularly so that if one becomes known by
an unauthorized party, the party has unauthorized access to the network
device only for a short time. Such access could allow an adversary to
disrupt ICS operations or monitor ICS network activity.
Inadequate access controls applied Unauthorized access to network devices and administrative functions could
allow a user to disrupt ICS operations or monitor ICS network activity.
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Table 3-9. Network Hardware Vulnerabilities
Inadequate physical protection of
network equipment
Access to network equipment should be controlled to prevent damage or
destruction.
Unsecured physical ports Unsecured universal serial bus (USB) and PS/2 ports could allow
unauthorized connection of thumb drives, keystroke loggers, etc.
Loss of environmental control Loss of environmental control could lead to processors overheating. Some
processors will shut down to protect themselves, and some just melt if they
overheat.
Non-critical personnel have access
to equipment and network
connections
Physical access to network equipment should be restricted to only the
necessary personnel. Improper access to network equipment can lead to
any of the following:
• Physical theft of data and hardware
• Physical damage or destruction of data and hardware
• Unauthorized changes to the security environment (e.g., altering
ACLs to permit attacks to enter a network)
• Unauthorized interception and manipulation of network activity
• Disconnection of physical data links or connection of unauthorized
data links
Lack of redundancy for critical
networks
Lack of redundancy in critical networks could provide single point of failure
possibilities
Table 3-10. Network Perimeter Vulnerabilities
No security perimeter defined If the control network does not have a security perimeter clearly defined,
then it is not possible to ensure that the necessary security controls are
deployed and configured properly. This can lead to unauthorized access to
systems and data, as well as other problems.
Firewalls nonexistent or improperly
configured
A lack of properly configured firewalls could permit unnecessary data to
pass between networks, such as control and corporate networks. This
could cause several problems, including allowing attacks and malware to
spread between networks, making sensitive data susceptible to
monitoring/eavesdropping on the other network, and providing individuals
with unauthorized access to systems.
Control networks used for non-
control traffic
Control and non-control traffic have different requirements, such as
determinism and reliability, so having both types of traffic on a single
network makes it more difficult to configure the network so that it meets the
requirements of the control traffic. For example, non-control traffic could
inadvertently consume resources that control traffic needs, causing
disruptions in ICS functions.
Control network services not within
the control network
Where IT services such as Domain Name System (DNS),and/or Dynamic
Host Configuration Protocol (DHCP) are used by control networks, they are
often implemented in the IT network, causing the ICS network to become
dependent on the IT network that may not have the reliability and availability
requirements needed by the ICS.
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Table 3-11. Network Monitoring and Logging Vulnerabilities
Inadequate firewall and router logs Without proper and accurate logs, it might be impossible to determine what
caused a security incident to occur.
No security monitoring on the ICS
network
Without regular security monitoring, incidents might go unnoticed, leading to
additional damage and/or disruption. Regular security monitoring is also
needed to identify problems with security controls, such as
misconfigurations and failures.
Table 3-12. Communication Vulnerabilities
Critical monitoring and control
paths are not identified
Rogue and/or unknown connections into the ICS can leave a backdoor for
attacks.
Standard, well-documented
communication protocols are used
in plain text
Adversaries that can monitor the ICS network activity can use a protocol
analyzer or other utilities to decode the data transferred by protocols such
as telnet, File Transfer Protocol (FTP), and Network File System (NFS).
The use of such protocols also makes it easier for adversaries to perform
attacks against the ICS and manipulate ICS network activity.
Authentication of users, data or
devices is substandard or
nonexistent
Many ICS protocols have no authentication at any level. Without
authentication, there is the potential to replay, modify, or spoof data or to
spoof devices such as sensors and user identities.
Lack of integrity checking for
communications
There are no integrity checks built into most industrial control protocols;
adversaries could manipulate communications undetected. To ensure
integrity, the ICS can use lower-layer protocols (e.g., IPsec) that offer data
integrity protection.
Table 3-13. Wireless Connection Vulnerabilities
Inadequate authentication between
clients and access points
Strong mutual authentication between wireless clients and access points is
needed to ensure that clients do not connect to a rogue access point
deployed by an adversary, and also to ensure that adversaries do not
connect to any of the ICS’s wireless networks.
Inadequate data protection
between clients and access points
Sensitive data between wireless clients and access points should be
protected using strong encryption to ensure that adversaries cannot gain
unauthorized access to the unencrypted data.
3.4 Risk Factors
Several factors currently contribute to the increasing risk to control systems, which are discussed in
greater detail in Sections 3.4.1 through 3.4.4:
Adoption of standardized protocols and technologies with known vulnerabilities
Connectivity of the control systems to other networks
Insecure and rogue connections
Widespread availability of technical information about control systems.
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3.4.1 Standardized Protocols and Technologies
ICS vendors have begun to open up their proprietary protocols and publish their protocol specifications to
enable third-party manufacturers to build compatible accessories. Organizations are also transitioning
from proprietary systems to less expensive, standardized technologies such as Microsoft Windows and
Unix-like operating systems as well as common networking protocols such as TCP/IP to reduce costs and
improve performance. Another standard contributing to this evolution of open systems is OPC, a protocol
that enables interaction between control systems and PC-based application programs. The transition to
using these open protocol standards provides economic and technical benefits, but also increases the
susceptibility of ICS to cyber incidents. These standardized protocols and technologies have commonly
known vulnerabilities, which are susceptible to sophisticated and effective exploitation tools that are
widely available and relatively easy to use.
3.4.2 Increased Connectivity
ICS and corporate IT systems are often interconnected as a result of several changes in information
management practices, operational, and business needs. The demand for remote access has encouraged
many organizations to establish connections to the ICS that enable ICS engineers and support personnel
to monitor and control the system from points outside the control network. Many organizations have also
added connections between corporate networks and ICS networks to allow the organization’s decision
makers to obtain access to critical data about the status of their operational systems and to send
instructions for the manufacture or distribution of product. In early implementations this might have been
done with custom applications software or via an OPC server/gateway; however, in the past ten years this
has been accomplished with Transmission Control Protocol/Internet Protocol (TCP/IP) networking and
standardized IP applications like File Transfer Protocol (FTP) or Extensible Markup Language (XML)
data exchanges. Often, these connections were implemented without a full understanding of the
corresponding security risks. In addition, corporate networks are often connected to strategic partner
networks and to the Internet. Control systems also make more use of WANs and the Internet to transmit
data to their remote or local stations and individual devices. This integration of control system networks
with public and corporate networks increases the accessibility of control system vulnerabilities. Unless
appropriate security controls are deployed, these vulnerabilities can expose all levels of the ICS network
architecture to complexity-induced error, adversaries and a variety of cyber threats, including worms and
other malware. As an example of the change in threats to control systems, an internal survey of an
unnamed energy organization showed the following:
The majority of the business units’ management believed their control systems were not connected to
the corporate network.
An audit showed the majority of the control systems were connected in some way to the corporate
network.
The corporate network was only secured to support general business processes and not safety-critical
systems.
Adding to the complexity of the situation, the goals of IT departments can be fundamentally different
from those of process control departments. The IT world typically sees performance, confidentiality, and
data integrity as paramount, while the ICS world sees human and plant safety as its primary
responsibility, and thus system availability and data integrity are core priorities. Other distinctions, as
discussed in Section 3.1, include differences in reliability requirements, incident impacts, performance
expectations, operating systems, communications protocols, and system architectures. This can mean
significant differences in implementation of security practices.
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3.4.3 Insecure and Rogue Connections
Many ICS vendors have delivered systems with dial-up modems that provide remote access to ease the
burdens of maintenance for the technical field support personnel. Remote access sometimes provides
support staff with administrative-level access to a system, such as using a telephone number, and
sometimes an access control credential (e.g., valid ID, and/or a password). Adversaries with war
dialers—simple personal computer programs that dial consecutive phone numbers looking for modems—
and password cracking software could gain access to systems through these remote access capabilities.
Passwords used for remote access are often common to all implementations of a particular vendor’s
systems and may have not been changed by the end user. These types of connections can leave a system
highly vulnerable because people entering systems through vendor-installed modems are often granted
high levels of system access.
Organizations often inadvertently leave access links such as dial-up modems open for remote diagnostics,
maintenance, and monitoring. Also, control systems increasingly utilize wireless communications
systems, which can be vulnerable. Access links not protected with authentication and/or encryption have
the increased risk of adversaries using these unsecured connections to access remotely controlled systems.
This could lead to an adversary compromising the integrity of the data in transit as well as the availability
of the system, both of which can result in an impact to public and plant safety. Before deploying
encryption, first determine if encryption is an appropriate solution for the specific ICS application.
Section 6.3.4.1 provides additional information on the use of encryption in the ICS environment.
Many of the interconnections between corporate networks and ICS require the integration of systems with
different communications standards. The result is often an infrastructure that is engineered to move data
successfully between two unique systems. Because of the complexity of integrating disparate systems,
control engineers often fail to address the added burden of accounting for security risks. Many control
engineers have little if any training in security and often IT security personnel are not involved in ICS
security design. As a result, access controls designed to protect control systems from unauthorized access
through corporate networks are usually minimal. Moreover, the behavior of the underlying protocols may
not be well understood, and thus vulnerabilities can exist that can defeat even advanced security
countermeasures. Protocols, such as TCP/IP and others have characteristics that often go unchecked, and
this may counter any security that can be done at the network or the application levels.
3.4.4 Public Information
Public information regarding ICS design, maintenance, interconnection, and communication is readily
available over the Internet to support competition in product choices as well as to enable the use of open
standards. ICS vendors also sell toolkits to help develop software that implements the various standards
used in ICS environments. There are also many former employees, vendors, contractors, and other end
users of the same ICS equipment worldwide who have inside knowledge about the operation of control
systems and processes. For example, one person used his inside knowledge of a system to cause one of
the most cited ICS cyber security incidents, the Maroochy Shire sewage spill. Additional information on
the Maroochy Shire sewage spill incident is available in Section 3.7.
Information and resources are available to potential adversaries and intruders of all calibers around the
world. With the available information, it is quite possible for an individual with very little knowledge of
control systems to gain unauthorized access to a control system with the use of automated attack and data
mining tools and a factory-set default password. Many times, these default passwords are never changed.
3-16

3.5 Possible Incident Scenarios
There are many possible incident scenarios for an ICS including [10]:
Control systems operation disrupted by delaying or blocking the flow of information through
corporate or control networks, thereby denying availability of the networks to control system
operators or causing information transfer bottlenecks or denial of service by IT-resident services
(such as DNS)
Unauthorized changes made to programmed instructions in PLCs, RTUs, DCS, or SCADA
controllers, alarm thresholds changed, or unauthorized commands issued to control equipment, which
could potentially result in damage to equipment (if tolerances are exceeded), premature shutdown of
processes (such as prematurely shutting down transmission lines), causing an environmental incident,
or even disabling control equipment
False information sent to control system operators either to disguise unauthorized changes or to
initiate inappropriate actions by system operators
Control system software or configuration settings modified, producing unpredictable results
Safety systems operation interfered with
Malicious software (e.g., virus, worm, Trojan horse) introduced into the system
Recipes (i.e., the materials and directions for creating a product) or work instructions modified in
order to bring about damage to products, equipment, or personnel
In addition, in control systems that cover a wide geographic area, the remote sites are often not staffed
and may not be physically monitored. If such remote systems are physically breached, the adversaries
could establish a connection back to the control network.
The following are two hypothetical ICS incident scenarios [11]:
Using war dialers—simple computer programs that dial consecutive phone numbers looking for
modems—an adversary finds modems connected to the programmable breakers of the electric power
transmission control system, cracks the passwords that control access to the breakers, and changes the
control settings to cause local power outages and damage equipment. The adversary lowers the
settings from 500 Ampere (A) to 200 A on some circuit breakers, taking those lines out of service and
diverting power to neighboring lines. At the same time, the adversary raises the settings on
neighboring lines to 900 A, preventing the circuit breakers from tripping, thus overloading the lines.
This causes significant damage to transformers and other critical equipment, resulting in lengthy
repair outages.
A power plant serving a large metropolitan district has logically isolated the control system from the
corporate network of the plant, installed state-of-the-art firewalls, and implemented intrusion
detection and prevention technology. An engineer innocently downloads information about a
continuing education seminar at a local college, inadvertently introducing a virus into the control
network. Just before the morning peak, the operator screens go blank and the system is shut down.
Although these scenarios are hypothetical, they represent potential incident scenarios for an ICS. Section
3.7 provides summaries of several actual ICS incidents.
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3.6 Sources of Incidents
An accurate accounting of cyber incidents on control systems is difficult to determine. However,
individuals in the industry who have been focusing on this issue see similar growth trends between
vulnerabilities exposed in traditional IT systems and those being found in control systems. There is a
Repository of Security Incidents (RISI)3
, which is designed to track incidents of a cyber security nature
that directly affect ICS and processes. This includes events such as accidental cyber-related incidents, as
well as deliberate events such as unauthorized remote access, DoS attacks, and malware infiltrations.
Data is collected through research into publicly known incidents and from private reporting by member
organizations that wish to have access to the database. Each incident is investigated and then rated
according to reliability (confirmed, likely but unconfirmed, unlikely or unknown, and hoax/urban legend).
The data collected includes the following:
Incident title
Date of incident
Reliability of report
Type of incident (e.g., accident, virus)
Industry (e.g., petroleum, automotive)
Entry point (e.g., Internet, wireless, modem)
Perpetrator
Type of system and hardware impacted
Brief description of incident
Impact on organization
Measures to prevent recurrence
References.
As of June 2006, 119 incidents had been investigated and logged in the database, with 15 incidents still
pending investigation. Of these, 13 were flagged as hoax or unlikely and removed from the study data.
Figure 3-1 shows the trend of incidents between 1982 and 2006, which shows a sharp increase in
incidents starting around 2001. The complexity of modern ICS leaves many vulnerabilities as well as
vectors for attack. Attacks can come from many places, including indirectly through the corporate
network or directly via the Internet, virtual private networks (VPN), wireless networks, and dial-up
modems.
3
The Repository of Security Incidents (RISI) can be found at: http://www.securityincidents.org/
3-18

Other sources of control system impact information show an increase in control system incidents as well.
It is not clear whether there are more incidents happening or just more are being detected and reported.
Figure 3-1. Industrial Security Incidents by Year
There are three broad categories of control system incidents:
Intentional targeted attacks such as gaining unauthorized access to files, performing a DoS, or
spoofing e-mails (i.e., forging the sender’s identity for an e-mail)
Unintentional consequences or collateral damage from worms, viruses or control system failures
Unintentional internal security consequences, such as inappropriate testing of operational systems or
unauthorized system configuration changes.
Of the three, targeted attacks are the least frequent. Targeted attacks are potentially the most damaging,
but also require detailed knowledge of the system and supporting infrastructure. Therefore, the most
likely threat agents are unintentional threats and disgruntled employees, former employees, and others
that have worked with or for the organization.[12].
3.7 Documented Incidents
As mentioned in Section 3.6, there are three broad categories of ICS incidents including intentional
attacks, unintentional consequences or collateral damage from worms, viruses or control system failures,
and unintentional internal security consequences, such as inappropriate testing of operational systems or
unauthorized system configuration changes. Reported incidents from these categories include the
following:
Intentional Attacks
Worcester Air Traffic Communications4
. In March 1997, a teenager in Worcester, Massachusetts
disabled part of the public switched telephone network using a dial-up modem connected to the
system. This knocked out phone service at the control tower, airport security, the airport fire
department, the weather service, and carriers that use the airport. Also, the tower’s main radio
transmitter and another transmitter that activates runway lights were shut down, as well as a printer
that controllers use to monitor flight progress. The attack also knocked out phone service to 600
homes and businesses in the nearby town of Rutland.
4
Additional information on the Worcester Air Traffic Communications incident can be found at:
http://www.cnn.com/TECH/computing/9803/18/juvenile.hacker/index.html
3-19

Maroochy Shire Sewage Spill5
. In the spring of 2000, a former employee of an Australian
organization that develops manufacturing software applied for a job with the local government, but
was rejected. Over a two-month period, the disgruntled rejected employee reportedly used a radio
transmitter on as many as 46 occasions to remotely break into the controls of a sewage treatment
system. He altered electronic data for particular sewerage pumping stations and caused malfunctions
in their operations, ultimately releasing about 264,000 gallons of raw sewage into nearby rivers and
parks.
Stuxnet Worm6
. Stuxnet is a Microsoft Windows computer worm discovered in July 2010 that
specifically targets industrial software and equipment. The worm initially spreads indiscriminately,
but includes a highly specialized malware payload that is designed to target only specific SCADA
systems that are configured to control and monitor specific industrial processes.
Unintentional Consequences
CSX Train Signaling System7
. In August 2003, the Sobig computer virus was blamed for shutting
down train signaling systems throughout the east coast of the U.S. The virus infected the computer
system at CSX Corp.’s Jacksonville, Florida headquarters, shutting down signaling, dispatching, and
other systems. According to Amtrak spokesman Dan Stessel, ten Amtrak trains were affected in the
morning. Trains between Pittsburgh and Florence, South Carolina were halted because of dark
signals, and one regional Amtrak train from Richmond, Virginia to Washington and New York was
delayed for more than two hours. Long-distance trains were also delayed between four and six hours.
Davis-Besse8
. In August 2003, the Nuclear Regulatory Commission confirmed that in January 2003,
the Microsoft SQL Server worm known as Slammer infected a private computer network at the idled
Davis-Besse nuclear power plant in Oak Harbor, Ohio, disabling a safety monitoring system for
nearly five hours. In addition, the plant’s process computer failed, and it took about six hours for it to
become available again. Slammer reportedly also affected communications on the control networks
of at least five other utilities by propagating so quickly that control system traffic was blocked.
Northeast Power Blackout9
. In August 2003, failure of the alarm processor in First Energy’s
SCADA system prevented control room operators from having adequate situational awareness of
critical operational changes to the electrical grid. Additionally, effective reliability oversight was
prevented when the state estimator at the Midwest Independent System Operator failed due to
incomplete information on topology changes, preventing contingency analysis. Several key 345 kV
transmission lines in Northern Ohio trip due to contact with trees. This eventually initiates cascading
overloads of additional 345 kV and 138 kV lines, leading to an uncontrolled cascading failure of the
grid. A total of 61,800 MW load was lost as 508 generating units at 265 power plants tripped.
5
Additional information on the Maroochy Shire Sewage Spill incident can be found at:
http://www.theregister.co.uk/2001/10/31/hacker_jailed_for_revenge_sewage/
6
Additional information on the Stuxnet worm can be found at: http://en.wikipedia.org/wiki/Stuxnet
7
Additional information on the CSX Train Signaling System incident can found at:
http://www.cbsnews.com/stories/2003/08/21/tech/main569418.shtml and
http://www.informationweek.com/story/showArticle.jhtml?articleID=13100807
8
Additional information on the Davis-Besse incident can found at: http://www.securityfocus.com/news/6767
9
Additional information on the Northeast Power Blackout incident can found at:
http://www.oe.energy.gov/DocumentsandMedia/BlackoutFinal-Web.pdf
3-20

Zotob Worm10
. In August 2005, a round of Internet worm infections knocked 13 of
DaimlerChrysler’s U.S. automobile manufacturing plants offline for almost an hour, stranding
workers as infected Microsoft Windows systems were patched. Plants in Illinois, Indiana, Wisconsin,
Ohio, Delaware, and Michigan were knocked offline. While the worm affected primarily Windows
2000 systems, it also affected some early versions of Windows XP. Symptoms include the repeated
shutdown and rebooting of a computer. Zotob and its variations caused computer outages at heavy-
equipment maker Caterpillar Inc., aircraft-maker Boeing, and several large U.S. news organizations.
Taum Sauk Water Storage Dam Failure11
. In December 2005, the Taum Sauk Water Storage Dam
suffered a catastrophic failure releasing a billion gallons of water. The failure of the reservoir
occurred as the reservoir was being filled to capacity or may have possibly been overtopped. The
current working theory is that the reservoir's berm was overtopped when the routine nightly pump-
back operation failed to cease when the reservoir was filled. According to AmerenUE, the gauges at
the dam read differently than the gauges at the Osage plant at the Lake of the Ozarks, which monitors
and operates the Taum Sauk plant remotely. The stations are linked together using a network of
microwave towers, and there are no operators on-site at Taum Sauk.
Bellingham, Washington Gasoline Pipeline Failure12
. In June 1999, 900,000 liters (237,000
gallons) of gasoline leaked from a 16” pipeline and ignited 1.5 hours later causing 3 deaths, 8 injuries,
and extensive property damage. The pipeline failure was exacerbated by control systems not able to
perform control and monitoring functions. “Immediately prior to and during the incident, the SCADA
system exhibited poor performance that inhibited the pipeline controllers from seeing and reacting to
the development of an abnormal pipeline operation.” A key recommendation from the NTSB report
issued October 2002 was to utilize an off-line development and testing system for implementing and
testing changes to the SCADA database.
10
Additional information on the Zotob Worm incident can found at: http://www.eweek.com/article2/0,1895,1849914,00.asp
and http://www.computerwire.com/industries/research/?pid=750E3094-C77B-4E85-AA27-2C1D26D919C7
11
Additional information on the Taum Sauk Water Storage Dam Failure incident can found at:
http://en.wikipedia.org/wiki/Taum_Sauk_Dam_Failure
12
Additional information on Bellingham, Washington Gasoline Pipeline Failure incident can found at
www.ntsb.gov/publictn/2002/PAR0202.pdf
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3-22
Unintentional Internal Security Consequences
Vulnerability Scanner Incidents13
. While a ping sweep was being performed on an active SCADA
network that controlled 3 meter (9 foot) robotic arms, it was noticed that one arm became active and
swung around 180 degrees. The controller for the arm was in standby mode before the ping sweep
was initiated. In a separate incident, a ping sweep was being performed on an ICS network to identify
all hosts that were attached to the network, for inventory purposes, and it caused a system controlling
the creation of integrated circuits in the fabrication plant to hang. This test resulted in the destruction
of $50,000 worth of wafers. See Section 4.2.6 for additional guidance on ICS vulnerability
assessments.
Penetration Testing Incident14
. A natural gas utility hired an IT security consulting organization to
conduct penetration testing on its corporate IT network. The consulting organization carelessly
ventured into a part of the network that was directly connected to the SCADA system. The
penetration test locked up the SCADA system and the utility was not able to send gas through its
pipelines for four hours. The outcome was the loss of service to its customer base for those four
hours.
13
Additional information on vulnerability scanner incidents can found at:
http://www.sandia.gov/scada/documents/sand_2005_2846p.pdf
14
Additional information on penetration testing incidents can found at:
http://www.sandia.gov/scada/documents/sand_2005_2846p.pdf

4. ICS Security Program Development and Deployment
As described in Section 3.1, there are critical operational differences between ICS and IT systems that
influence how specific security controls should be applied to the ICS. Accordingly, organizations should
develop and deploy an ICS security program.15
ICS security plans and programs should be consistent
with and integrated with existing IT security experience, programs, and practices, but must be tailored to
the specific requirements and characteristics of ICS technologies and environments. Organizations
should review and update their ICS security plans and programs regularly to reflect changes in
technologies, operations, standards, and regulations, as well as the security needs of specific facilities.
This section provides an overview of the development and deployment of an ICS security program.
Section 4.1 describes how to establish a business case for an ICS security program, including suggested
content for the business case. Section 4.2 discusses the development of a comprehensive ICS security
program and provides information on several major steps in deploying the program. Information on
specific security controls that might be implemented as part of the security program is given in Sections 5
and 6 of the document.
4.1 Business Case for Security
The first step in implementing a cyber security program for ICS is to develop a compelling business case
for the unique needs of the organization. The business case should capture the business concerns of
senior management while being founded in the experience of those who are already dealing with many of
the same risks. The business case provides the business impact and financial justification for creating an
integrated cyber security program. It should include detailed information about the following:
Benefits, including improved control system reliability and availability, of creating an integrated
security program
Prioritized potential costs and damage scenarios if a cyber security program for the ICS is not
implemented
High-level overview of the process required to implement, operate, monitor, review, maintain, and
improve the cyber security program
Costs and resources required to develop, implement and maintain the security program.
Before presenting the business case to management, there should be a well-thought-out and developed
security implementation and cost plan. For example, simply requesting a firewall is insufficient for
numerous reasons.
4.1.1 Benefits
Responsible risk management policy mandates that the threat to the ICS should be measured and
monitored to protect the interests of employees, the public, shareholders, customers, vendors, and society.
Risk analysis enables costs and benefits to be weighed so that informed decisions can be made on
protective actions. In addition to reducing risks, exercising due-diligence and displaying responsibility
also helps organizations by:
Improving control system reliability and availability
15
The Instrumentation, Systems, and Automation (ISA) 99 Committee http://www.isa.org/isa99 has developed ANSI/ISA-
99.02.01-2009, a standard that addresses the development and deployment of an ICS security program in detail.
4-1

Improving employee morale, loyalty, and retention
Reducing community concerns
Increasing investor confidence
Reducing legal liabilities
Enhancing the corporate image and reputation
Helping with insurance coverage and cost
Improving investor and banking relations.
A strong safety and cyber security management program is fundamental to a sustainable business model.
4.1.2 Potential Consequences
The importance of secure systems should be further emphasized as business reliance on interconnectivity
increases. DoS attacks and malware (e.g., worms, viruses) have become all too common and have
already impacted ICS. In addition, a cyber breach in some critical infrastructures can have significant
physical impacts. The major categories of impacts are as follows:
Physical Impacts. Physical impacts encompass the set of direct consequences of ICS failure. The
potential effects of paramount importance include personal injury and loss of life. Other effects
include the loss of property (including data) and potential damage to the environment.
Economic Impacts. Economic impacts are a second-order effect from physical impacts ensuing
from an ICS incident. Physical impacts could result in repercussions to system operations, which in
turn inflict a greater economic loss on the facility or organization. On a larger scale, these effects
could negatively impact the local, regional, national, or possibly global economy.
Social Impacts. Another second-order effect, the consequence from the loss of national or public
confidence in an organization, is many times overlooked. It is, however, a very real target and one
that could be accomplished through an ICS incident.
Potential consequences of an ICS incident are listed below. Note that items in this list are not
independent. In fact, one can lead to another. For example, release of hazardous material can lead to
injury or death.
Impact on national security—facilitate an act of terrorism
Reduction or loss of production at one site or multiple sites simultaneously
Injury or death of employees
Injury or death of persons in the community
Damage to equipment
Release, diversion, or theft of hazardous materials
Environmental damage
Violation of regulatory requirements
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Product contamination
Criminal or civil legal liabilities
Loss of proprietary or confidential information
Loss of brand image or customer confidence.
Undesirable incidents of any sort detract from the value of an organization, but safety and security
incidents can have longer-term negative impacts than other types of incidents on all stakeholders—
employees, shareholders, customers, and the communities in which an organization operates.
4.1.3 Key Components of the Business Case
There are four key components of the business case: prioritized threats, prioritized business
consequences, prioritized business benefits, and estimated annual business impact.
4.1.3.1 Prioritized Threats
The list of potential threats provided in Section 3.2 needs to be refined to those threats that the
organization believes could reasonably impact the facility to be secured. For instance, a food and
beverage organization might not find terrorism a credible threat but might be more concerned with
viruses, worms, and disgruntled employees.
4.1.3.2 Prioritized Business Consequences
The list of potential business consequences provided in Section 4.1.2 needs to be distilled to the particular
business consequences that senior management will find the most compelling. For instance, a food and
beverage organization that handles no toxic or flammable materials and typically processes its product at
relatively low temperatures and pressures might not be concerned about equipment damage or
environmental impact, but might be more concerned about loss of production availability and degradation
of product quality. Regulatory compliance might also be a concern. Individuals should not minimize the
potential consequences to avoid taking proper security risk mitigation actions.
The Sarbanes-Oxley Act requires corporate leaders to sign off on compliance with information accuracy
and protection of corporate information.16
Also, the demonstration of due diligence is required by most
internal and external audit firms to satisfy shareholders and other organization stakeholders. By
implementing a comprehensive cyber security program, management is exercising due diligence.
4.1.3.3 Prioritized Business Benefits
Improved control systems security and control system specific security policies can potentially improve
control system reliability and availability. This also includes minimizing unintentional control system
cyber security impacts from inappropriate testing, policies, and misconfigured systems.
4.1.3.4 Estimated Annual Business Impact
The highest priority items shown in the list of prioritized business consequences should be evaluated to
obtain an estimate of the annual business impact, preferably but not necessarily in financial terms. For
the food and beverage organization example, the organization may have experienced a virus incident
within its internal network that the information security staff estimated as resulting in a specific financial
16
More information on the act, and a copy of the act itself, can be found at http://www.sec.gov/about/laws.shtml.
4-3

cost. If the internal network and the control network are interconnected, it is conceivable that a virus
originating from the control network could cause the same amount of business impact. NIST SP 800-39
[19] and ISO/IEC 27002 provide additional guidance on business impact.
4.1.4 Resources for Building Business Case
The main resources for information to help form a business case are external resources in trade and
standards organizations, consulting firms and internal resources in related risk management programs or
engineering and operations. External resources in trade and standards organizations can often provide
useful tips as to what factors most strongly influenced their management to support their efforts and what
resources within their organizations proved most helpful. For different industries, these factors may be
different, but there may be similarities in the roles that other risk management specialists can play.
Appendix C provides a list and short description of some of the current activities in ICS security.
Internal resources in related risk management efforts (e.g., information security, health, safety and
environmental risk, physical security, business continuity) can provide tremendous assistance based on
their experience with related incidents in the organization. This information is helpful from the
standpoint of prioritizing threats and estimating business impact. These resources can also provide
insight into which managers are focused on dealing with which risks and, thus, which managers might be
the most appropriate or receptive to serving as a champion. Internal resources in control systems
engineering and operations can provide insight into the details of how control systems are deployed
within the organization, such as the following:
How networks are typically segregated
What remote access connections are generally employed
How high-risk control systems or safety instrumented systems are typically designed
What security countermeasures are commonly used
4.1.5 Presenting the Business Case to Leadership
The business leadership will be responsible for approving and driving cyber security policies, assigning
security roles, and implementing the cyber security program across the organization. Funding for the
entire program can usually be done in phases. While some funding may be required to start the cyber
security activity, additional funding can be obtained later as the security vulnerabilities and needs of the
program are better understood and additional strategies are developed. Additionally, the costs (both direct
and indirect) should be considered for retrofitting the ICS for security vs. addressing security to begin
with.
Often, a good approach to obtain management buy-in to address the problem is to ground the business
case in a successful actual third-party example. The business case should present to management that the
other organization had the same problem and then present that they found a solution and how they solved
it. This will often prompt management to ask what the solution is and how it might be applicable to their
organization.
4.2 Developing a Comprehensive Security Program
Effectively integrating security into an ICS requires defining and executing a comprehensive program that
addresses all aspects of security, ranging from identifying objectives to day-to-day operation and ongoing
4-4

auditing for compliance and improvement. This section describes the basic process for developing a
security program, including the following:
Obtain senior management buy-in
Build and train a cross-functional team
Define charter and scope
Define specific ICS policies and procedures
Define and inventory ICS assets
Perform a risk and vulnerability assessment
Define the mitigation controls
Provide training and raise security awareness for ICS staff.
More detailed information on the various steps is provided in ANSI/ISA-99.02.01 Security for Industrial
Automation and Control Systems: Establishing an Industrial Automation and Control Systems Security
Program.
The commitment to a security program begins at the top. Senior management must demonstrate a clear
commitment to cyber security. Cyber security is a business responsibility shared by all members of the
enterprise and especially by leading members of the business, process, and management teams. Cyber
security programs with adequate funding and visible, top-level support from organization leaders are
more likely to achieve compliance, function more smoothly, and have greater success than programs that
do not have that support.
Whenever a new system is being designed and installed, it is imperative to take the time to address
security throughout the lifecycle, from architecture to procurement to installation to maintenance to
decommissioning. There are serious risks in deploying systems to production based on the assumption
that they will be secured later. If there is insufficient time and resources to secure the system properly
before deployment, it is unlikely that there will be sufficient time and resources later to address security.
4.2.1 Senior Management Buy-in
It is critical for the success of the ICS security program that senior management [29] buy into and
participate in the ICS security program. Senior management needs to be at a level that encompasses both
IT and ICS operations.
4.2.2 Build and Train a Cross-Functional Team
It is essential for a cross-functional cyber security team to share their varied domain knowledge and
experience to evaluate and mitigate risk in the ICS. At a minimum, the cyber security team should consist
of a member of the organization’s IT staff, a control engineer, a control system operator, security subject
matter experts, and a member of the management staff. Security knowledge and skills should include
network architecture and design, security processes and practices, and secure infrastructure design and
operation. For continuity and completeness, the cyber security team should also include the control
system vendor and/or system integrator. The cyber security team should report directly to site
management (e.g., facility superintendent) or the company’s CIO/CSO, who in turn, accepts complete
4-5

responsibility and accountability for the cyber security of the ICS. Management level accountability will
help ensure an ongoing commitment to cyber security efforts.
While the control engineers will play a large role in securing the ICS, they will not be able to do so
without collaboration and support from both the IT department and management. IT often has years of
security experience, much of which is applicable to ICS. As the cultures of control engineering and IT
are often significantly different and unknown to the other party, significant cross-cultural understanding
and integration will be essential for the development of a collaborative security design and operation.
4.2.3 Define Charter and Scope
The cyber security team should establish the corporate policy that defines the guiding charter of the
security organization and the roles, responsibilities, and accountabilities of system owners and users. The
team should decide upon and document the objective of the security program, the business organizations
affected, all the computer systems and networks involved, the budget and resources required, and the
division of responsibilities. The scope can also address business, training, audit, legal, and regulatory
requirements, as well as timetables and responsibilities.
There may already be a program in place or being developed for the organization’s IT business systems.
The team should identify which existing practices to leverage and which practices are specific to the
control system. In the long run, it will be easier to get positive results if the team can share resources with
others in the organization that have similar objectives.
4.2.4 Define ICS Specific Security Policies and Procedures
Policies and procedures are at the root of every successful security program and wherever possible, ICS
specific security polices and procedures should be integrated with existing operational/management
policies. The more transparent these policies are with all other procedures, the more likely they will be
implemented at all levels. Policies and procedures help to ensure that security protection is both
consistent and current to protect against evolving threats, and also help to educate. After the risks for the
various systems are clearly understood, the cyber security team should examine existing security policies
to see if they adequately address the risks to the ICS. If needed, existing policies should be revised or
new policies created to address desktop and business systems as well as the ICS. Few organizations have
the resources to harden the ICS against all possible threats; management should guide the development of
the security policies, based on a risk assessment that will set the security priorities and goals for the
organization so that the risks posed by the threats are mitigated sufficiently. Procedures that support the
policies need to be developed so that the policies are implemented fully and properly for the ICS.
Security procedures should be documented, tested, and updated periodically in response to policy and
technology changes. Consider developing ICS security policies and procedures based on the Homeland
Security Advisory System Threat Level, deploying increasingly heightened security postures as the
Threat Level increases.
4.2.5 Define and Inventory ICS Systems and Networks Assets
The cyber security team should identify the applications and computer systems within the ICS, as well as
the networks within and interfacing to the ICS. The focus should be on systems rather than just devices,
and should include PLCs, DCS, SCADA, and instrument-based systems that use a monitoring device such
as an HMI. Assets that use a routable protocol or are dial-up accessible should be documented. As the
team identifies the ICS assets, the information should be recorded in a standard format. The team should
review and update the ICS asset list annually.
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There are several commercial enterprise inventory tools that can identify and document all hardware and
software resident on a network. Care must be taken before using these tools to identify ICS assets; teams
should first conduct an assessment of how these tools work and what impact they might have on the
connected control equipment. Tool evaluation may include testing in similar, non-production control
system environments to ensure that the tools do not adversely impact the production systems. Impact
could be due to the nature of the information or the volume of network traffic. While this impact may be
acceptable in IT systems, it is not acceptable in an ICS. Additional information and guidance on scanning
and inventory tools is provided in Section 4.2.6.
4.2.6 Perform Risk and Vulnerability Assessment
Because every organization has a limited set of resources, organizations should perform a risk assessment
for the ICS systems and use its results to prioritize the ICS systems based on the potential impact to each
system. The organization should then perform a detailed vulnerability assessment for the highest-priority
systems and assessments for lower-priority systems as deemed prudent/as resources allow. The
vulnerability assessment will help identify any weaknesses that may be present in the systems that could
allow the confidentiality, integrity, or availability of systems and data to be adversely affected, along with
the related cyber security risks and mitigation approaches to reduce the risks.
Because of the potential for disruption to the devices, vulnerability scanners should be used with caution
on production ICS networks [30]. A major concern is an accidental DoS to devices and networks.
Vulnerability scanners often attempt to verify vulnerabilities by extensively probing and conducting a
representative set of attacks against devices and networks. ICS were designed and built to control and
automate real-world processes or equipment. Given the wrong instructions, they could perform incorrect
actions, causing product loss, equipment damage, injury, or even deaths.
The following examples [31] demonstrate the danger:
While a ping sweep was being performed on an active SCADA network that controlled 9-foot robotic
arms, it was noticed that one arm became active and swung around 180 degrees. The controller for
the arm was in standby mode before the ping sweep was initiated.
On an ICS network, a ping sweep was being performed to identify all hosts that were attached to the
network, for inventory purposes, and it caused a system controlling the creation of integrated circuits
in the fabrication plant to lock-up. This test resulted in the destruction of $50,000 worth of wafers.
A natural gas utility hired an IT security consulting organization to conduct penetration testing on its
corporate IT network. The consulting organization carelessly ventured into a part of the network that
was directly connected to the SCADA system. The penetration test locked up the SCADA system
and the utility was not able to send gas through its pipelines for four hours. The outcome was the loss
of service to its customer base for those four hours.
Identifying the vulnerabilities within an ICS requires a different approach from that of a typical IT
system. In most cases, devices on an IT system can be rebooted, restored, or replaced with little
interruption of service to its customers. An ICS controls a physical process and therefore has real-world
consequences associated with its actions. Some actions are time-critical, while others have a more
relaxed timeframe.
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When performing an inventory or vulnerability scan on a system or network segment, there are several
steps that are generally performed. Each step is listed in Table 4-1, along with the usual IT action and
alternate suggested actions that should be taken instead for an ICS, making the outcomes of any testing
safer. These techniques may make the work somewhat more difficult, but should help to mitigate
problems associated with active scanning.
Table 4-1. Suggested Actions for ICS Vulnerability Assessments
To Be Identified Usual IT Action Suggested ICS Actions
Hosts, nodes, and
networks
Ping sweep (e.g., nmap) • Examine router configuration files or route tables
• Perform physical verification (chasing wires)
• Conduct passive network listening or use intrusion
detection (e.g., snort) on the network
• Specify a subset of IP addresses to be programmatically
scanned
Services Port scan (e.g., nmap) • Do local port verification (e.g., netstat)
• Scan a duplicate, development, or test system on a non-
production network
Vulnerabilities
within a service
Vulnerability scan (e.g.,
nessus)
• Perform local banner grabbing with version lookup in
Common Vulnerabilities and Exposures (CVE)
• Scan a duplicate, development, or test system on a non-
production network
The commonality among the suggested ICS actions is that they do not generate traffic on production
operational networks or against production systems. These less intrusive methods can gather most, if not
all, of the same information as more active methods, without the risk of causing a failure during testing.
Another factor to consider when choosing ICS testing methods is that these systems have little spare
capacity as compared to IT systems. ICS systems have much greater longevity than their IT counterparts,
so their hardware is often well behind the state-of-the-art and can be easily overtaxed. Also, ICS systems
usually run at slow speeds on legacy networks that can be overwhelmed by the volume of traffic
generated during active testing.
When any assessment of an ICS is being performed, ICS personnel must be aware that testing is
occurring, and be prepared to immediately address any problems that arise. If manual control of the
system is possible, personnel capable of performing manual control should be present during the security
testing. Additionally, security auditors need to understand the ICS under test, the risk involved with the
test, and the consequences associated with unintentional stimulus or DoS to the ICS.
4.2.7 Define the Mitigation Controls
Organizations should analyze the detailed risk assessment, identify the cost of mitigation for each risk,
compare the cost with the risk of occurrence, and select those mitigation controls where cost is less than
the potential risk. Because it is usually impractical or impossible to eliminate all risks, organizations
should focus on mitigating risk with the greatest potential impact to the ICS and the process.
The controls to mitigate a specific risk may vary among types of systems. For example, user
authentication controls might be different for ICS than for corporate payroll systems and e-commerce
systems. Organizations should document and communicate the selected controls, along with the
procedures for using the controls. As the team identifies mitigation strategies, risks may be identified that
can be mitigated by “quick fix” solutions—low-cost, high-value practices that can significantly reduce
risk. Examples of these solutions are restricting Internet access and eliminating e-mail access on operator
control stations or consoles. Organizations should identify, evaluate, and implement suitable quick fix
solutions as soon as possible to reduce security risks and achieve rapid benefits. The Department of
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Energy (DOE) has a “21 Steps to Improve Cyber Security of SCADA Networks” [32] document that
could be used as a starting point to outline specific actions to increase the security of SCADA systems
and other ICS.
4.2.8 Provide Training and Raise Security Awareness
Security awareness is a critical part of ICS incident prevention, particularly when it comes to social
engineering threats. Social engineering is a technique used to manipulate individuals into giving away
private information, such as passwords. This information can then be used to compromise otherwise
secure systems.
Implementing an ICS security program may bring changes to the way in which personnel access
computer programs, applications, and the computer desktop itself. Organizations should design effective
training and awareness programs and communication vehicles to help employees understand why new
access and control methods are required, ideas they can use to reduce risks, and the impact on the
organization if control methods are not incorporated. Training programs also demonstrate management’s
commitment to, and the value of, a cyber security program. Feedback from staff exposed to this type of
training can be a valuable source of input for refining the charter and scope of the security program.

5. Network Architecture
When designing a network architecture for an ICS deployment, it is usually recommended to separate the
ICS network from the corporate network. The nature of network traffic on these two networks is
different: Internet access, FTP, e-mail, and remote access will typically be permitted on the corporate
network but should not be allowed on the ICS network. Rigorous change control procedures for network
equipment, configuration, and software changes may not be in place on the corporate network. If ICS
network traffic is carried on the corporate network, it could be intercepted or be subjected to a DoS attack.
By having separate networks, security and performance problems on the corporate network should not be
able to affect the ICS network.
Practical considerations often mean that a connection is required between the ICS and corporate
networks. This connection is a significant security risk and careful consideration should be given to the
design and implementation. If the networks must be connected, it is strongly recommended that only
minimal (single if possible) connections be allowed and that the connection is through a firewall and a
DMZ. A DMZ is a separate network segment that connects directly to the firewall. Servers containing
the data from the ICS that needs to be accessed from the corporate network are put on this network
segment. Only these systems should be accessible from the corporate network. With any external
connections, the minimum access should be permitted through the firewall, including opening only the
ports required for specific communication. The following sections describe the access required for
specific node types.
5.1 Firewalls
Network firewalls are devices or systems that control the flow of network traffic between networks
employing differing security postures. In most modern applications, firewalls and firewall environments
are discussed in the context of Internet connectivity and the TCP/IP protocol suite. However, firewalls
have applicability in network environments that do not include or require Internet connectivity. For
example, many corporate networks employ firewalls to restrict connectivity to and from internal networks
servicing more sensitive functions, such as the accounting or human resource departments. By employing
firewalls to control connectivity to these areas, an organization can prevent unauthorized access to the
respective systems and resources within the more sensitive areas. There are three general classes of
firewalls:
Packet Filtering Firewalls. The most basic type of firewall is called a packet filter. Packet filter
firewalls are essentially routing devices that include access control functionality for system addresses
and communication sessions. The access control is governed by a set of directives collectively
referred to as a rule set. In their most basic form, packet filters operate at layer 3 (network) of the
Open Systems Interconnection (OSI) model. This type of firewall checks basic information in each
packet, such as IP addresses, against a set of criteria before forwarding the packet. Depending on the
packet and the criteria, the firewall can drop the packet, forward it, or send a message to the
originator. The advantages of packet filtering firewalls include low cost and low impact on network
performance, usually because only one or a few header fields in the packet are examined.
Stateful Inspection Firewalls. Stateful inspection firewalls are packet filters that incorporate added
awareness of the OSI model data at layer 4. Stateful inspection firewalls filter packets at the network
layer, determine whether session packets are legitimate, and evaluate the contents of packets at the
transport layer (e.g., TCP, UDP) as well. Stateful inspection keeps track of active sessions and uses
that information to determine if packets should be forwarded or blocked. It offers a high level of
security and good performance, but it may be more expensive and complex to administer. Additional
rule sets for ICS applications may be required.
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Application-Proxy Gateway Firewalls. This class of firewalls examines packets at the application
layer and filters traffic based on specific application rules, such as specified applications (e.g.,
browsers) or protocols (e.g., FTP). It offers a high level of security, but could have overhead and
delay impacts on network performance, which can be unacceptable in an ICS environment.
NIST SP 800-41, Guidelines on Firewalls and Firewall Policy, provides general guidance for the
selection of firewalls and the firewall policies.
In an ICS environment, firewalls are most often deployed between the ICS network and the corporate
network [33]. Properly configured, they can greatly restrict undesired access to and from control system
host computers and controllers, thereby improving security. They can also potentially improve a control
network’s responsiveness by removing non-essential traffic from the network. When properly designed,
configured, and maintained, dedicated hardware firewalls can contribute significantly to increasing the
security of today’s ICS environments.
Firewalls provide several tools to enforce a security policy that cannot be accomplished locally on the
current set of process control devices available in the market, including the ability to:
Block all communications with the exception of specifically enabled communications between
devices on the unprotected LAN and protected ICS networks. Blocking is based on source and
destination IP address pairs, services, and ports. Blocking can occur on both inbound and outbound
packets, which is helpful in limiting high-risk communications such as e-mail.
Enforce secure authentication of all users seeking to gain access to the ICS network. There is
flexibility to employ varying protection levels of authentication methods including simple passwords,
complex passwords, multi-factor authentication technologies, tokens, biometrics and smart cards.
Select the particular method based upon the vulnerability of the ICS network to be protected, rather
than using the method that is available at the device level.
Enforce destination authorization. Users can be restricted and allowed to reach only the nodes on the
control network necessary for their job function. This reduces the potential of users intentionally or
accidentally gaining access to and control of devices for which they are not authorized, but adds to
the complexity for on-the-job-training or cross-training employees.
Record information flow for traffic monitoring, analysis, and intrusion detection.
Permit the ICS to implement operational policies appropriate to the ICS but that might not be
appropriate in an IT network, such as prohibition of less secure communications like email, and
permitted use of easy-to-remember usernames and group passwords.
Be designed with documented and minimal (single if possible) connections that permit the ICS
network to be severed from the corporate network, should that decision be made, in times of serious
cyber incidents.
Other possible deployments include using either host-based firewalls or small standalone hardware
firewalls in front of, or running on, individual control devices. Using firewalls on an individual device
basis can create significant management overhead, especially in change management of firewall
configurations.
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There are several issues that must be addressed when deploying firewalls in ICS environments,
particularly the following:
The possible addition of delay to control system communications
The lack of experience in the design of rule sets suitable for industrial applications. Firewalls used to
protect control systems should be configured so they do not permit either incoming or outgoing traffic
by default. The default configuration should only be modified when it is necessary to permit
connections to or from trusted systems.
Hardware firewalls require ongoing support, maintenance, and backup. Rule sets need to be reviewed to
make sure that they are providing adequate protection in light of ever-changing security threats. System
capabilities (e.g., storage space for firewall logs) should be monitored to make sure that the firewall is
performing its data collection tasks and can be depended upon in the event of a security violation. Real-
time monitoring of firewalls and other security sensors is required to rapidly detect and initiate response
to cyber incidents.
5.2 Logically Separated Control Network
The ICS network should, at a minimum, be logically separated from the corporate network on physically
separate network devices. When enterprise connectivity is required:
There should be documented and minimal (single if possible) access points between the ICS network
and the corporate network. Redundant (i.e., backup) access points, if present, must be documented.
A stateful firewall between the ICS network and corporate network should be configured to deny all
traffic except that which is explicitly authorized.
The firewall rules should at a minimum provide source and destination filtering (i.e., filter on media
access control [MAC] address), in addition to TCP and User Datagram Protocol (UDP) port filtering
and Internet Control Message Protocol (ICMP) type and code filtering.
An acceptable approach to enabling communication between an ICS network and a corporate network is
to implement an intermediate DMZ network. The DMZ should be connected to the firewall such that
specific (restricted) communication may occur between only the corporate network and the DMZ, and the
ICS network and the DMZ. The corporate network and the ICS network should not communicate directly
with each other. This approach is described in Sections 5.3.4 and 5.3.5. Additional security may be
obtained by implementing a Virtual Private Network (VPN) between the ICS and external networks.
Sections 5.8.2 and 6.3.4.2 provide additional information on the use of VPNs.
5.3 Network Segregation
ICS networks and corporate networks can be segregated to enhance cyber security using different
architectures. This section describes several possible architectures and explains the advantages and
disadvantages of each. Please note that the intent of the diagrams in Section 5.3 is to show the placement
of firewalls to segregate the network. Not all devices that would be typically found on the control
network or corporate network are shown. Section 5.4 provides guidance on a recommended defense-in-
depth architecture.
5.3.1 Dual-Homed Computer/Dual Network Interface Cards (NIC)
Dual-homed computers can pass network traffic from one network to another. A computer without
proper security controls could pose additional threats. To prevent this, no systems other than firewalls
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should be configured as dual-homed to span both the control and corporate networks. All connections
between the control network and the corporate network should be through a firewall.
5.3.2 Firewall between Corporate Network and Control Network
By introducing a simple two-port firewall between the corporate and control networks, as shown in Figure
5-1, a significant security improvement can be achieved. Properly configured, a firewall significantly
reduces the chance of a successful external attack on the control network.
Unfortunately, two issues still remain with this design. First, if the data historian resides on the corporate
network, the firewall must allow the data historian to communicate with the control devices on the control
network. A packet originating from a malicious or incorrectly configured host on the corporate network
(appearing to be the data historian) would be forwarded to individual PLCs/DCS.
Figure 5-1. Firewall between Corporate Network and Control Network
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If the data historian resides on the control network, a firewall rule must exist that allows all hosts from the
enterprise to communicate with the historian. Typically, this communication occurs at the application
layer as Structured Query Language (SQL) or Hypertext Transfer Protocol (HTTP) requests. Flaws in the
historian’s application layer code could result in a compromised historian. Once the historian is
compromised, the remaining nodes on the control network are vulnerable to a worm propagating or an
interactive attack.
Another issue with having a simple firewall between the networks is that spoofed packets can be
constructed that can affect the control network, potentially permitting covert data to be tunneled in
allowed protocols. For example, if HTTP packets are allowed through the firewall, then Trojan horse
software accidentally introduced on an HMI or control network laptop could be controlled by a remote
entity and send data (such as captured passwords) to that entity, disguised as legitimate traffic.
In summary, while this architecture is a significant improvement over a non-segregated network, it
requires the use of firewall rules that allow direct communications between the corporate network and
control network devices. This can result in possible security breaches if not very carefully designed and
monitored [34].
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5.3.3 Firewall and Router between Corporate Network and Control Network
A slightly more sophisticated design, shown in Figure 5-2, is the use of a router/firewall combination.
The router sits in front of the firewall and offers basic packet filtering services, while the firewall handles
the more complex issues using either stateful inspection or proxy techniques. This type of design is very
popular in Internet-facing firewalls because it allows the faster router to handle the bulk of the incoming
packets, especially in the case of DoS attacks, and reduces the load on the firewall. It also offers
improved defense-in-depth because there are two different devices an adversary must bypass [34].
Figure 5-2. Firewall and Router between Corporate Network and Control Network
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5.3.4 Firewall with DMZ between Corporate Network and Control Network
A significant improvement is the use of firewalls with the ability to establish a DMZ between the
corporate and control networks. Each DMZ holds one or more critical components, such as the data
historian, the wireless access point, or remote and third party access systems. In effect, the use of a
DMZ-capable firewall allows the creation of an intermediate network.
Creating a DMZ requires that the firewall offer three or more interfaces, rather than the typical public and
private interfaces. One of the interfaces is connected to the corporate network, the second to the control
network, and the remaining interfaces to the shared or insecure devices such as the data historian server or
wireless access points on the DMZ network. Figure 5-3 provides an example of this architecture.
Figure 5-3. Firewall with DMZ between Corporate Network and Control Network
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By placing corporate-accessible components in the DMZ, no direct communication paths are required
from the corporate network to the control network; each path effectively ends in the DMZ. Most firewalls
can allow for multiple DMZs, and can specify what type of traffic may be forwarded between zones. As
Figure 5-3 shows, the firewall can block arbitrary packets from the corporate network from entering the
control network, and can also regulate traffic from the other network zones including the control network.
With well-planned rule sets, a clear separation can be maintained between the control network and other
networks, with little or no traffic passing directly between the corporate and control networks.
If a patch management server, an antivirus server, or other security server is to be used for the control
network, it should be located directly on the DMZ. Both functions could reside on a single server.
Having patch management and antivirus management dedicated to the control network allows for
controlled and secure updates that can be tailored for the unique needs of the ICS environment. It may
also be helpful if the antivirus product chosen for ICS protection is not the same as the antivirus product
used for the corporate network. For example, if a malware incident occurs and one antivirus product
cannot detect or stop the malware, it is somewhat likely that another product may have that capability.
The primary security risk in this type of architecture is that if a computer in the DMZ is compromised,
then it can be used to launch an attack against the control network via application traffic permitted from
the DMZ to the control network. This risk can be greatly reduced if a concerted effort is made to harden
and actively patch the servers in the DMZ and if the firewall rule set permits only connections between
the control network and DMZ that are initiated by control network devices. Other concerns with this
architecture are the added complexity and the potential increased cost of firewalls with several ports. For
more critical systems, however, the improved security should more than offset these disadvantages [34].
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5.3.5 Paired Firewalls between Corporate Network and Control Network
A variation on the firewall with DMZ solution is to use a pair of firewalls positioned between the
corporate and ICS networks, as shown in Figure 5-4. Common servers such as the data historian are
situated between the firewalls in a DMZ-like network zone sometimes referred to as a Manufacturing
Execution System (MES) layer. As in the architectures described previously, the first firewall blocks
arbitrary packets from proceeding to the control network or the shared historians. The second firewall
can prevent unwanted traffic from a compromised server from entering the control network, and prevent
control network traffic from impacting the shared servers.
Figure 5-4. Paired Firewalls between Corporate Network and Control Network
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If firewalls from two different manufacturers are used, then this solution may offer an advantage. It also
allows the control group and the IT group to have clearly separated device responsibility because each can
manage a firewall on its own, if the decision is made within the organization to do so. The primary
disadvantage with two-firewall architectures is the increased cost and management complexity. For
environments with stringent security requirements or the need for clear management separation, this
architecture has some strong advantages.
5.3.6 Network Segregation Summary
In summary, non-firewall-based solutions will generally not provide suitable isolation between control
networks and corporate networks. The two-zone solutions (no DMZ) are marginally acceptable but
should only be deployed with extreme care. The most secure, manageable, and scalable control network
and corporate network segregation architectures are typically based on a system with at least three zones,
incorporating one or more DMZs.
5.4 Recommended Defense-in-Depth Architecture
A single security product, technology or solution cannot adequately protect an ICS by itself. A multiple
layer strategy involving two (or more) different overlapping security mechanisms, a technique also known
as defense-in-depth, is desired so that the impact of a failure in any one mechanism is minimized. A
defense-in-depth architecture strategy includes the use of firewalls, the creation of demilitarized zones,
intrusion detection capabilities along with effective security policies, training programs and incident
response mechanisms. In addition, an effective defense-in-depth strategy requires a thorough
understanding of possible attack vectors on an ICS. These include:
Backdoors and holes in network perimeter
Vulnerabilities in common protocols
Attacks on field devices
Database attacks
Communications hijacking and ‘man-in-the-middle’ attacks
Figure 5-5 shows an ICS defense-in-depth architecture strategy that has been developed by the DHS
Control Systems Security Program (CSSP) Recommended Practices committee17
as described in the
Control Systems Cyber Security: Defense in Depth Strategies [35] document. Additional supporting
documents that cover specific issues and associated mitigations are also included on the site. This site will
continue to evolve and grow as new recommended practices and related information are added.
The Control Systems Cyber Security: Defense in Depth Strategies document provides guidance and
direction for developing defense-in-depth architecture strategies for organizations that use control system
networks while maintaining a multi-tier information architecture that requires:
Maintenance of various field devices, telemetry collection, and/or industrial-level process systems
Access to facilities via remote data link or modem
Public facing services for customer or corporate operations
17
Information on the CSSP Recommended Practices is located at http://www.us-cert.gov/control_systems/practices/.
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This strategy includes firewalls, the use of demilitarized zones and intrusion detection capabilities
throughout the ICS architecture. The use of several demilitarized zones in Figure 5-5 provides the added
capability to separate functionalities and access privileges and has proved to be very effective in
protecting large architectures comprised of networks with different operational mandates. Intrusion
detection deployments apply different rule-sets and signatures unique to each domain being monitored.
Figure 5-5. CSSP Recommended Defense-In-Depth Architecture
5.5 General Firewall Policies for ICS
Once the defense-in-depth architecture is in place, the work of determining exactly what traffic should be
allowed through the firewalls begins. Configuring the firewalls to deny all except for the traffic
absolutely required for business needs is every organization’s basic premise, but the reality is much more
difficult. Exactly what does “absolutely required for business” mean and what are the security impacts of
allowing that traffic through? For example, many organizations considered allowing SQL traffic through
the firewall as required for business for many data historian servers. Unfortunately, SQL was also the
vector for the Slammer worm. Many important protocols used in the industrial world, such as HTTP,
FTP, OPC/DCOM, EtherNet/IP, and MODBUS/TCP, have significant security vulnerabilities.
The remaining material in this section summarizes some of the key points from the CPNI Good Practice
Guide on Firewall Deployment for SCADA and Process Control Networks [34] document.
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When installing a single two-port firewall without a DMZ for shared servers (i.e., the architecture
described in Section 5.3.2), particular care needs to be taken with the rule design. At a minimum, all rules
should be stateful rules that are both IP address and port (application) specific. The address portion of the
rules should restrict incoming traffic to a very small set of shared devices (e.g., the data historian) on the
control network from a controlled set of addresses on the corporate network. Allowing any IP addresses
on the corporate network to access servers inside the control network is not recommended. In addition,
the allowed ports should be carefully restricted to relatively secure protocols such as Hypertext Transfer
Protocol Secure (HTTPS). Allowing HTTP, FTP, or other unsecured protocols to cross the firewall is a
security risk due to the potential for traffic sniffing and modification. Rules should be added to deny
hosts outside the control network from initiating connections with hosts on the control network. Rules
should only allow devices internal to the control network the ability to establish connections outside the
control network.
On the other hand, if the DMZ architecture is being used, then it is possible to configure the system so
that no traffic will go directly between the corporate network and the control network. With a few special
exceptions (noted below), all traffic from either side can terminate at the servers in the DMZ. This allows
more flexibility in the protocols allowed through the firewall. For example, MODBUS/TCP might be
used to communicate from the PLCs to the data historian, while HTTP might be used for communication
between the historian and enterprise clients. Both protocols are inherently insecure, yet in this case they
can be used safely because neither actually crosses between the two networks. An extension to this
concept is the idea of using “disjoint” protocols in all control network to corporate network
communications. That is, if a protocol is allowed between the control network and DMZ, then it is
explicitly not allowed between the DMZ and corporate network. This design greatly reduces the chance
of a worm such as Slammer actually making its way into the control network, because the worm would
have to use two different exploits over two different protocols.
One area of considerable variation in practice is the control of outbound traffic from the control network,
which could represent a significant risk if unmanaged. One example is Trojan horse software that uses
HTTP tunneling to exploit poorly defined outbound rules. Thus, it is important that outbound rules be as
stringent as inbound rules.
A summary of these follows:
Inbound traffic to the control system should be blocked. Access to devices inside the control system
should be through a DMZ.
Outbound traffic through the control network firewall should be limited to essential communications
only.
All outbound traffic from the control network to the corporate network should be source and
destination-restricted by service and port.
In addition to these rules, the firewall should be configured with outbound filtering to stop forged IP
packets from leaving the control network or the DMZ. In practice this is achieved by checking the source
IP addresses of outgoing packets against the firewall’s respective network interface address. The intent is
to prevent the control network from being the source of spoofed (i.e., forged) communications, which are
often used in DoS attacks. Thus, the firewalls should be configured to forward IP packets only if those
packets have a correct source IP address for the control network or DMZ networks. Finally, Internet
access by devices on the control network should be strongly discouraged.
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In summary, the following should be considered as recommended practice for general firewall rule sets:
The base rule set should be deny all, permit none.
Ports and services between the control network environment and the corporate network should be
enabled and permissions granted on a specific case-by-case basis. There should be a documented
business justification with risk analysis and a responsible person for each permitted incoming or
outgoing data flow.
All “permit” rules should be both IP address and TCP/UDP port specific, and stateful if appropriate.
All rules should restrict traffic to a specific IP address or range of addresses.
Traffic should be prevented from transiting directly from the control network to the corporate
network. All traffic should terminate in the DMZ.
Any protocol allowed between the control network and DMZ should explicitly NOT be allowed
between the DMZ and corporate networks (and vice-versa).
All outbound traffic from the control network to the corporate network should be source and
destination-restricted by service and port.
Outbound packets from the control network or DMZ should be allowed only if those packets have a
correct source IP address that is assigned to the control network or DMZ devices.
Control network devices should not be allowed to access the Internet.
Control networks should not be directly connected to the Internet, even if protected via a firewall.
All firewall management traffic should be carried on either a separate, secured management network
(e.g., out of band) or over an encrypted network with multi-factor authentication. Traffic should also
be restricted by IP address to specific management stations.
These should only be considered as guidelines. A careful assessment of each control environment is
required before implementing any firewall rule sets.
5.6 Recommended Firewall Rules for Specific Services
Beside the general rules described above, it is difficult to outline all-purpose rules for specific protocols.
The needs and recommended practices vary significantly between industries for any given protocol and
should be analyzed on an organization-by-organization basis. The Industrial Automation Open
Networking Association (IAONA) offers a template for conducting such an analysis [36], assessing each
of the protocols commonly found in industrial environments in terms of function, security risk, worst case
impact, and suggested measures. Below are summarized some of the key points from the IAONA
document. The reader is advised to consult this document directly when developing rule sets.
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5.6.1 Domain Name System (DNS)
Domain Name System (DNS) is primarily used to translate between domain names and IP addresses. For
example, a DNS could map a domain name such as control.com to an IP address such as 192.168.1.1.
Most Internet services rely heavily on DNS, but its use on the control network is relatively rare at this
time. In most cases there is little reason to allow DNS requests out of the control network to the corporate
network and no reason to allow DNS requests into the control network. DNS requests from the control
network to DMZ should be addressed on a case-by-case basis. Local DNS or the use of host files is
recommended.
5.6.2 Hypertext Transfer Protocol (HTTP)
HTTP is the protocol underlying Web browsing services on the Internet. Like DNS, it is critical to most
Internet services. It is seeing increasing use on the plant floor as well as an all-purpose query tool.
Unfortunately, it has little inherent security, and many HTTP applications have vulnerabilities that can be
exploited. HTTP can be a transport mechanism for many manually performed attacks and automated
worms.
In general, HTTP should not be allowed to cross from the corporate to the control network. If it is, then
HTTP proxies should be configured on the firewall to block all inbound scripts and Java applications.
Incoming HTTP connections should not be allowed into the control network, as they pose significant
security risks. If HTTP services into the control network are absolutely required, it is recommended that
the more secure HTTPS be used instead and only to specific devices.
5.6.3 FTP and Trivial File Transfer Protocol (TFTP)
FTP and Trivial File Transfer Protocol (TFTP) are used for transferring files between devices. They are
implemented on almost every platform including many SCADA systems, DCS, PLCs, and RTUs, because
they are very well known and use minimum processing power. Unfortunately, neither protocol was
created with security in mind; for FTP, the login password is not encrypted, and for TFTP, no login is
required at all. Furthermore, some FTP implementations have a history of buffer overflow vulnerabilities.
As a result, all TFTP communications should be blocked, while FTP communications should be allowed
for outbound sessions only or if secured with additional token-based multi-factor authentication and an
encrypted tunnel. More secure protocols, such as Secure FTP (SFTP) or Secure Copy (SCP), should be
employed whenever possible.
5.6.4 Telnet
The telnet protocol defines an interactive, text-based communications session between a client and a host.
It is mainly used for remote login and simple control services to systems with limited resources or to
systems with limited needs for security. It is a severe security risk because all telnet traffic, including
passwords, is unencrypted, and it can allow a remote individual considerable control over a device.
Inbound telnet sessions from the corporate to the control network should be prohibited unless secured
with token-based multi-factor authentication and an encrypted tunnel. Outbound telnet sessions should be
allowed only over encrypted tunnels (e.g., VPN) to specific devices.
5.6.5 Simple Mail Transfer Protocol (SMTP)
SMTP is the primary e-mail transfer protocol on the Internet. E-mail messages often contain malware, so
inbound e-mail should not be allowed to any control network device. Outbound SMTP mail messages
from the control network to the corporate network are acceptable to send alert messages.
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5.6.6 Simple Network Management Protocol (SNMP)
SNMP is used to provide network management services between a central management console and
network devices such as routers, printers, and PLCs. Although SNMP is an extremely useful service for
maintaining a network, it is very weak in security. Versions 1 and 2 of SNMP use unencrypted
passwords to both read and configure devices (including devices such as PLCs), and in many cases the
passwords are well known and cannot be changed. Version 3 is considerably more secure but is still
limited in use. SNMP V1 & V2 commands both to and from the control network should be prohibited
unless it is over a separate, secured management network whereas SNMP V3 commands may be able to
be sent to the ICS using the security features inherent to V3.
5.6.7 Distributed Component Object Model (DCOM)
DCOM is the underlying protocol for both OLE for Process Control (OPC) and ProfiNet. It utilizes
Microsoft’s Remote Procedure Call (RPC) service which, when not patched, has many vulnerabilities.
These vulnerabilities were the basis for the Blaster worm exploits. In addition, OPC, which utilizes
DCOM, dynamically opens a wide range of ports (1024 to 65535) that can be extremely difficult to filter
at the firewall. This protocol should only be allowed between control network and DMZ networks and
explicitly blocked between the DMZ and corporate network. Also, users are advised to restrict the port
ranges used by making registry modifications on devices using DCOM.
5.6.8 SCADA and Industrial Protocols
SCADA and industrial protocols, such as MODBUS/TCP, EtherNet/IP, and DNP3
18
, are critical for
communications to most control devices. Unfortunately, these protocols were designed without security
built in and do not typically require any authentication to remotely execute commands on a control
device. These protocols should only be allowed within the control network and not allowed to cross into
the corporate network.
5.7 Network Address Translation (NAT)
Network address translation (NAT) is a service where IP addresses used on one side of a network device
can be mapped to a different set on the other side on an as-needed basis. It was originally designed for IP
address reduction purposes so that an organization with a large number of devices that occasionally
needed Internet access could get by with a smaller set of assigned Internet addresses.
To do this, most NAT implementations rely on the premise that not every internal device is actively
communicating with external hosts at a given moment. The firewall is configured to have a limited
number of outwardly visible IP addresses. When an internal host seeks to communicate to an external
host, the firewall remaps the internal IP address and port to one of the currently unused, more limited,
public IP addresses, effectively concentrating outgoing traffic into fewer IP addresses. The firewall must
track the state of each connection and how each private internal IP address and source port was remapped
onto an outwardly visible IP address/port pair. When returning traffic reaches the firewall, the mapping is
reversed and the packets forwarded to the proper internal host.
For example, a control network device may need to establish a connection with an external, non-control
network host (for instance, to send a critical alert e-mail). NAT allows the internal IP address of the
initiating control network host to be replaced by the firewall; subsequent return traffic packets are
18
The DNP User Group is currently performing work in conjunction with IEC 62351 to extend the DNP3 protocol to provide
strong authentication.
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remapped back to the internal IP address and sent to the appropriate control network device. More
specifically, if the control network is assigned the private subnet 192.168.1.xxx and the Internet network
expects the device to use the corporate assigned addresses in the range 192.6.yyy.zzz, then a NAT
firewall will substitute (and track) a 192.6.yyy.zzz source address into every outbound IP packet
generated by a control network device.
Producer-consumer protocols, such as EtherNet/IP and Foundation Fieldbus, are particularly troublesome
because NAT does not support the multicast-based traffic that these protocols need to offer their full
services.
In general, while NAT offers some distinct advantages, its impact on the actual industrial protocols and
configuration should be assessed carefully before it is deployed. Furthermore, certain protocols are
specifically broken by NAT because of the lack of direct addressing. For example, OPC requires special
third-party tunneling software to work with NAT.
5.8 Specific ICS Firewall Issues
In addition to the issues with firewalls and ICS already discussed, there are some additional problems that
need to be examined in more detail. The rest of this section discusses three specific areas of concern: the
placement of data historians, remote access for ICS support, and multicast traffic.
5.8.1 Data Historians
The existence of shared control network/corporate network servers such as data historians and asset
management servers can have a significant impact on firewall design and configuration. In three-zone
systems the placement of these servers in a DMZ is relatively straightforward, but in two-zone designs the
issues become complex. Placing the historian on the corporate side of the firewall means that a number
of insecure protocols, such as MODBUS/TCP or DCOM, must be allowed through the firewall and that
every control device reporting to the historian is exposed to the corporate side of the network. On the
other hand, putting the historian on the control network side means other equally questionable protocols,
such as HTTP or SQL, must be allowed through the firewall, and there is now a server accessible to
nearly everyone in the organization sitting on the control network.
In general, the best solution is to avoid two-zone systems (no DMZ) and use a three-zone design, placing
the data collector in the control network and the historian component in the DMZ; however, even this can
prove problematic in some situations. Heavy access from the large numbers of users on the corporate
network to a historian in the DMZ may tax the firewall’s throughput capabilities. One potential solution
is to install two servers: one on the control network to collect data from the control devices, and a second
on the corporate network mirroring the first server and supporting client queries. The issue of how to
time synchronize both historians will have to be addressed. This also requires a special hole to be put
through the firewall to allow direct server-to-server communications, but if done correctly, this poses only
minor risk.
5.8.2 Remote Support Access
Another issue for ICS firewall design is user and/or vendor remote access into the control network. Any
users accessing the control network from remote networks should be required to authenticate using an
appropriately strong mechanism such as token-based authentication. While it is possible for the controls
group to set up their own remote access system with multi-factor authentication on the DMZ, in most
organizations it is typically more efficient to use existing systems set up by the IT department. In this
case a connection through the firewall from the IT remote access server is needed.
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Remote support personnel connecting over the Internet or via dialup modems should use an encrypted
protocol, such as running a corporate VPN connection client, application server, or secure HTTP access,
and authenticate using a strong mechanism, such as a token based multi-factor authentication scheme, in
order to connect to the general corporate network. Once connected, they should be required to
authenticate a second time at the control network firewall using a strong mechanism, such as a token
based multi-factor authentication scheme, to gain access to the control network. For organizations that do
not allow any control traffic to traverse the corporate network in the clear, this could require a cascading,
or secondary tunneling solutions, to gain access to the control network, such as a Secure Sockets Layer
(SSL) or Transport Layer Security (TLS) VPN inside an IPsec VPN.
5.8.3 Multicast Traffic
Most industrial producer-consumer (or publisher-subscriber) protocols operating over Ethernet, such as
EtherNet/IP and Foundation Fieldbus HSE, are IP multicast-based. The first advantage of IP multicasting
is network efficiency; by not repeating the data transmission to the multiple destinations, a significant
reduction in network load can occur. The second advantage is that the sending host need not be
concerned with knowing every IP address of every destination host listening for the broadcast
information. The third, and perhaps most important for industrial control purposes, is that a single
multicast message offers far better capabilities for time synchronization between multiple control devices
than multiple unicast messages.
If the source and destinations of a multicast packet are connected with no intervening routers or firewalls
between them, the multicast transmission is relatively seamless. However, if the source and destinations
are not on the same LAN, forwarding the multicast messages to a destination becomes more complicated.
To solve the problem of multicast message routing, hosts need to join (or leave) a group by informing the
multicast router on their network of the relevant group ID through the use of the Internet Group
Management Protocol (IGMP). Multicast routers subsequently know of the members of multicast groups
on their network and can decide whether or not to forward a received multicast message onto their
network. A multicast routing protocol is also required. From a firewall administration perspective,
monitoring and filtering IGMP traffic becomes another series of rule sets to manage, adding to the
complexity of the firewall.
Another firewall issue related to multicasting is the use of NAT. A firewall performing NAT that
receives a multicast packet from an external host has no reverse mapping for which internal group ID
should receive the data. If IGMP-aware, it could broadcast it to every group ID it knows about, because
one of them will be correct, but this could cause serious issues if an unintended control packet were
broadcast to a critical node. The safest action for the firewall to take is to drop the packet. Thus,
multicasting is generally considered NAT-unfriendly.
5.9 Single Points of Failure
Single points of failure can exist at any level of the ANSI/ISO stack. An example is PLC control of
safety interlocks. Because security is usually being added to the ICS environment, an evaluation should
be done to identify potential failure points and a risk assessment done to evaluate each point’s exposure.
Remediation methods can then be postulated and evaluated and a “risk versus reward” determination
made and design and implementation done.
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5.10 Redundancy and Fault Tolerance
ICS components or networks that are classified as critical to the organization have high availability
requirements. One method of achieving high availability is through the use of redundancy. Additionally,
if a component fails, it should fail in a manner that does not generate unnecessary traffic on the ICS, or
does not cause another problem elsewhere, such as a cascading event.
The control system should have the ability to execute an appropriate fail-safe process upon the loss of
communications with the ICS or the loss of the ICS itself. The organization should define what "loss of
communications" means (e.g., 5 seconds, 5 minutes, etc. without communications). The organization
should then, based on potential consequences, define the appropriate fail-safe process for their industry.
Backups should be performed using the “backup-in-depth” approach, with layers of backups (e.g., local,
facility, disaster) that are time-sequenced such that rapid recent local backups are available for immediate
use and secure backups are available to recover from a massive security incident. A mixture of
backup/restore approaches and storage methods should be used to ensure that backups are rigorously
produced, securely stored, and appropriately accessible for restoration.
5.11 Preventing Man-in-the-Middle Attacks
A man-in-the-middle attack requires knowledge of the protocol being manipulated. The Address
Resolution Protocol (ARP) man-in-the-middle attack is a popular method for an adversary to gain access
to the network flow of information on a target system. This is performed by attacking the network ARP
cache tables of the controller and the workstation machines. Using the compromised computer on the
control network, the adversary poisons the ARP tables on each host and informs them that they must
route all their traffic through a specific IP and hardware address (i.e., the adversary’s machine). By
manipulating the ARP tables, the adversary can insert his machine between the two target machines
and/or devices.
The ARP man-in-the-middle attack works by initiating gratuitous ARP commands to confuse each host
(i.e., ARP poisoning). These ARP commands cause each of the two target hosts to use the MAC address
of the adversary as the address for the other target host. When a successful man-in-the-middle attack is
performed, the hosts on each side of the attack are unaware that their network data is taking a different
route through the adversary’s computer.
Once an adversary has successfully inserted their machine into the information stream, they now have full
control over the data communications and could carry out several types of attacks. One possible attack
method is the replay attack. In its simplest form, captured data from the control/HMI is modified to
instantiate activity when received by the device controller. Captured data reflecting normal operations in
the ICS could be played back to the operator as required. This would cause the operator’s HMI to appear
to be normal and the attack will go unobserved. During this replay attack the adversary could continue to
send commands to the controller and/or field devices to cause an undesirable event while the operator is
unaware of the true state of the system.
Another attack that could be carried out with the man-in-the-middle attack is sending false messages to
the operator, and could take the form of a false negative or a false positive. This may cause the operator to
take an action, such as flipping a breaker, when it is not required, or it may cause the operator to think
everything is fine and not take an action when an action is required. The adversary could send commands
to the operator’s console indicating a system change, and when the operator follows normal procedures
and attempts to correct the problem, the operator’s action could cause an undesirable event. There are
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5-19
numerable variations of the modification and replay of control data which could impact the operations of
the system.
Protocol manipulation and the man-in-the-middle attack are among the most popular ways to manipulate
insecure protocols, such as those found in control systems. However, there are mitigation techniques [37]
that can be applied to secure the systems through MAC address locking, static tables, encryption, and
monitoring.
MAC Address Locking - The ARP man-in-the-middle attack requires the adversary to be connected
to the local network or have control of a local computer on the network. Port security, also called
MAC address locking, is one method to secure the physical connection at the end of each port on a
network switch. High-end corporate class network switches usually have some kind of option for
MAC address locking. MAC address locking is very effective against a rogue individual looking to
physically plug into the internal network. Without port security, any open network jack on the wall
could be used as an avenue onto the corporate network. Port security locks a specific MAC address to
a specific port on a managed switch. If the MAC address does not match, the communication link is
disabled and the intruder will not be able to achieve his goal. Some of the more advanced switches
have an auto resetting option, which will reset the security measure if the original MAC is returned to
the port.
Although port security is not attacker proof, it does add a layer of added security to the physical
network. It also protects the local network from employees plugging un-patched and out-of-date
systems onto the protected network. This reduces the number of target computers a remote adversary
can access. These security measures not only protect against attacks from external networks but
provide added physical protection as well.
Static Tables – An ICS network that stays relatively static could attempt to implement statically
coded ARP tables. Most operating systems have the capability to statically code all of the MAC
addresses into the ARP table on each computer. Statically coding the ARP tables on each computer
prevents the adversary from changing them by sending ARP reply packets to the victim computer.
While this technique is not feasible on a large and/or dynamic corporate network, the limited number
of hosts on an ICS network could be effectively protected this way.
Encryption - As a longer term solution, systems should be designed to include encryption between
devices in order to make it very difficult to reverse engineer protocols and forge packets on control
system networks. Encrypting the communications between devices would make it nearly impossible
to perform this attack. Protocols that provide strong authentication also provide resilience to man-in-
the-middle attacks.
Monitoring - Monitoring for ARP poisoning provides an added layer of defense. There are several
programs available (e.g., ARPwatch) that can monitor for changing MAC addresses through the ARP
packets.

6. ICS Security Controls
Security controls are the management, operational, and technical controls (i.e., safeguards or
countermeasures) prescribed for an informational system to protect the confidentiality, integrity, and
availability of the system and its information. This section discusses the security controls specified in
NIST SP 800-53, which was developed as part of the FISMA implementation project. See Appendix E
for additional information regarding FISMA and the NIST-led implementation project.
NIST SP 800-53 provides guidelines for selecting and specifying security controls for information
systems in support of Federal government information systems. Security controls are organized into three
classes; management, operational, and technical controls. Each class is broken into several families of
controls; each control contains a definition of the control, supplemental guidance, and possible
enhancements that will increase the strength of a basic control.
NIST has initiated the Industrial Control System Security Project19
in cooperation with the public and
private sector ICS community to develop specific guidance on the application of NIST documents,
including the security controls in NIST SP 800-53 to ICS. To facilitate the understanding of this
approach, an effort is underway to develop a series of ICS cyber security case histories using actual ICS
cyber security incidents. These case histories examine the NIST SP 800-53 ICS controls that were
violated or not implemented, and postulate the potential mitigations that may have occurred if the controls
had been implemented. ICS specific recommendations and guidance, if available, is provided in an
outlined box for each set of controls in this section.
A single security product or technology cannot adequately protect an ICS. Securing an ICS is based on a
combination of effective security policies and a properly configured set of security controls. An effective
cyber security strategy for an ICS should apply defense-in-depth, a technique of layering security
mechanisms so that the impact of a failure in any one mechanism is minimized. Use of such a strategy is
explored within the security control discussions and their applications to ICS that follow.
6.1 Management Controls
Management controls are the security countermeasures for an ICS that focus on the management of risk
and the management of information security. NIST SP 800-53 defines five families of controls within the
Management controls class:
Security Assessment and Authorization (CA): assurance that the specified controls are
implemented correctly, operating as intended, and producing the desired outcome.
Planning (PL): development and maintenance of a plan to address information system security by
performing assessments, specifying and implementing security controls, assigning security levels, and
responding to incidents
Risk Assessment (RA): the process of identifying risks to operations, assets, or individuals by
determining the probability of occurrence, the resulting impact, and additional security controls that
would mitigate this impact
System and Services Acquisition (SA): allocation of resources for information system security to be
maintained throughout the systems life cycle and the development of acquisition policies based on
risk assessment results including requirements, design criteria, test procedures, and associated
documentation
19
6-1

Program Management (PM): provides security controls at the organizational rather than the
information-system level.
These management controls are discussed in more detail in the sections to follow. ICS specific
recommendations and guidance, if available, is provided in an outlined box for each section.
6.1.1 Security Assessment and Authorization
The security controls that fall within the NIST SP 800-53 Assessment and Authorization (CA) family
provide the basis for performing periodic assessments and providing certification of the security controls
implemented in the information system to determine if the controls are implemented correctly, operating
as intended, and producing the desired outcome to meet the system security requirements. A senior
organizational official is responsible for accepting residual risk and authorizing system operation. These
steps constitute accreditation. In addition, all security controls should be monitored on an ongoing basis.
Monitoring activities include configuration management and control of information system components,
security impact analysis of changes to the system, ongoing assessment of security controls, and status
reporting.
Supplemental guidance for the CA controls can be found in the following documents:
NIST SP 800-12 provides guidance on security policies and procedures [38].
NIST SP 800-26 and 800-53A provide guidance on security control assessments [18][22].
NIST SP 800-37 provides guidance defining the information system boundary and security
certification and accreditation of the information system [20].
6.1.2 Planning
A security plan is a formal document that provides an overview of the security requirements for an
information system and describes the security controls in place or planned for meeting those
requirements. The security controls that fall within the NIST SP 800-53 Planning (PL) family provide the
basis for developing a security plan. These controls also address maintenance issues for periodically
updating a security plan. A set of rules describes user responsibilities and expected behavior regarding
information system usage with provision for signed acknowledgement from users indicating that they
have read, understand, and agree to abide by the rules of behavior before authorizing access to the
information system.
Supplemental guidance for the PL controls can be found in the following documents:
NIST SP 800-18 provides guidance on preparing rules of behavior [17].
ICS Specific Recommendations and Guidance
A security plan for an ICS should build on appropriate existing IT security experience, programs, and
practices. However, the critical differences between IT and ICS addressed in Section 3.1 will influence
how security will be applied to the ICS. A forward-looking plan is needed to provide a method for
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continuous security improvements. Whenever a new system is being designed and installed, it is
imperative to take the time to address security throughout the lifecycle, from architecture to
procurement to installation to maintenance to decommissioning. ICS security is a rapidly evolving
field requiring the security planning process to constantly explore emerging ICS security capabilities as
well as new threats that are identified by organizations such as the US-CERT Control Systems Security
Center (CSSC).
6.1.3 Risk Assessment
Risk is a function of the likelihood of a given threat source exploiting a potential vulnerability and the
resulting impact of a successful exploitation of the vulnerability. Risk assessment is the process of
identifying risks to an organization’s operations, assets, and individuals by determining the probability
that an identified vulnerability will be exploited and the resulting impact. An assessment includes an
evaluation of security controls that can mitigate each threat and the costs associated with implementing
them. A risk assessment must also compare the cost of security with the costs associated with an
incident.
Achieving an acceptable level of risk is a process of reducing the probability of an incident that is
accomplished by mitigating or eliminating vulnerabilities that can be exploited as well as consequences
resulting from an incident. Prioritization of vulnerabilities must be based on cost and benefit with an
objective to provide a business case for implementing at least a minimum set of control system security
requirements to reduce risk to an acceptable level. A mistake often made during a risk assessment is to
select technically interesting vulnerabilities without taking into account the level of risk associated with
them. Vulnerabilities should be assessed and rated for risk before trying to select and implement security
controls on them.
The security controls that fall within the NIST SP 800-53 Risk Assessment (RA) family provide policy
and procedures to develop, distribute, and maintain a documented risk assessment policy that describes
purpose, scope, roles, responsibilities, and compliance as well as policy implementation procedures. An
information system and associated data is categorized based on the security objectives and a range of risk
levels. A risk assessment is performed to identify risks and the magnitude of harm that could result from
the unauthorized access, use, disclosure, disruption, modification, or destruction of an information system
and data. Also included in these controls are mechanisms for keeping risk assessments up-to-date and
performing periodic testing and vulnerability assessments.
In the FISMA Risk Framework shown in Figure E-1 in Appendix E, the risk assessment process is
applied after the Security Categorization activity and baseline Security Control Selection activity. Risk
assessment is performed in the Security Control Refinement activity to determine if the selected security
controls need to be enhanced or expanded beyond the baseline security controls. NIST SP 800-30, Risk
Management Guide for Information Technology Systems (currently under revision) provides a risk
assessment methodology, which includes the following steps:
1. System characterization – produces a picture of the information system environment, and
delineation of system boundaries
2. Threat identification – produces a threat statement containing a list of threat-sources that could
exploit system vulnerabilities
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3. Vulnerability identification – produces a list of the system vulnerabilities that could be exercised
by the potential threat sources
4. Control analysis – produces a list of the planned controls used for the information system to
mitigate the likelihood of a vulnerability being exercised and reduce the impact of such an
adverse event.
5. Likelihood determination – produces a likelihood rating (High, Medium, or Low) that indicates
the probability that a potential vulnerability may be exercised
6. Impact analysis – produces a magnitude of impact (High, Medium, or Low) resulting from the
exploitation of a vulnerability.
7. Risk determination – produces measurement for risk based on a scale of High, Medium, or Low
8. Control recommendations – produces recommendations of security controls and alternative
solutions to mitigate risk
9. Results documentation – produces a risk assessment report that describes the threats and
vulnerabilities, measurement of risk, and provides recommendations for control implementation.
Supplemental guidance for the RA controls can be found in the following documents:
NIST SP 800-39 provides guidance on conducting risk assessments and updates [19].
NIST SP 800-40 provides guidance on handling security patches [39].
NIST SP 800-115 provides guidance on network security testing [40].
NIST SP 800-60 provides guidance on determining security categories for information types [24].
Organizations must consider the potential consequences resulting from an incident on an ICS. Well-
defined policies and procedures lead to mitigation techniques designed to thwart incidents and manage
the risk to eliminate or minimize the consequences. The potential degradation of the physical plant,
economic status, or stakeholder/national confidence could justify mitigation. For an ICS, a very
important aspect of the risk assessment is to determine the value of the data that is flowing from the
control network to the corporate network. In instances where pricing decisions are determined from
this data, the data could have a very high value. The fiscal justification for mitigation has to be derived
by comparing the mitigation cost to the effects of the consequence. However, it is not possible to
define a one-size-fits-all set of security requirements. A very high level of security may be achievable
but undesirable in many situations because of the loss of functionality and other associated costs. A
well-thought-out security implementation is a balance of risk versus cost. In some situations the risk
may be safety, health, or environment-related rather than purely economic. The risk may result in an
unrecoverable consequence rather than a temporary financial setback
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6.1.4 System and Services Acquisition
The security controls that fall within the NIST SP 800-53 System and Services Acquisition (SA) family
provide the basis for developing policies and procedures for acquisition of resources required to
adequately protect an information system. These acquisitions are based on security requirements and
security specifications. As part of the acquisition procedures, an information system is managed using a
system development life cycle methodology that includes information security considerations. As part of
acquisition, adequate documentation must be maintained on the information system and constituent
components.
The SA family also addresses outsourced systems and the inclusion of adequate security controls by
vendors as specified by the supported organization. Vendors are also responsible for configuration
management and security testing for these outsourced information systems.
Supplemental guidance for the SA controls can be found in the following documents:
NIST SP 800-23 provides guidance on the acquisition and use of tested/evaluated information
technology products [41].
NIST SP 800-27 provides guidance on engineering principles for information system security [42].
NIST SP 800-35 provides guidance on information technology security services [43].
NIST SP 800-36 provides guidance on the selection of information security products [44].
NIST SP 800-64 provides guidance on security considerations in the system development life cycle
[45].
NIST SP 800-65 provides guidance on integrating security into the capital planning and investment
control process [46].
NIST SP 800-70 provides guidance on configuration settings for information technology products
[25].
The security requirements of an organization outsourcing the management and control of all or some of
its information systems, networks, and desktop environments should be addressed in a contract agreed
between the parties. External suppliers that have an impact on the security of the organization must be
held to the same security policies and procedures to maintain the overall level of ICS security. Security
policies and procedures of second and third-tier suppliers should also be in compliance with corporate
cyber security policies and procedures in the case that they impact ICS security.
The SCADA and Control System Procurement Project [47] has developed a procurement language for
specifying security requirements when procuring new systems or maintaining existing systems.
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6.1.5 Program Management
The security controls that fall within the NIST SP 800-53 Program Management (PM) focus on the
organization-wide information security requirements that are independent of any particular information
system and are essential for managing information security programs.
6.2 Operational Controls
Operational controls are the security countermeasures for an ICS that are primarily implemented and
executed by people as opposed to systems. NIST SP 800-53 defines nine families of controls within the
Operational controls class:
Personnel Security (PS): policies and procedures for personnel position categorization, screening,
transfer, penalty, and termination; also addresses third-party personnel security.
Physical and Environmental Protection (PE): policies and procedures addressing physical,
transmission, and display access control as well as environmental controls for conditioning (e.g.,
temperature, humidity) and emergency provisions (e.g., shutdown, power, lighting, fire protection).
Contingency Planning (CP): policies and procedures designed to maintain or restore business
operations, including computer operations, possibly at an alternate location, in the event of
emergencies, system failures, or disaster.
Configuration Management (CM): policies and procedures for controlling modifications to
hardware, firmware, software, and documentation to ensure the information system is protected
against improper modifications prior to, during, and after system implementation.
Maintenance (MA): policies and procedures to manage all maintenance aspects of an information
system.
System and Information Integrity (SI): policies and procedures to protect information systems and
their data from design flaws and data modification using functionality verification, data integrity
checking, intrusion detection, malicious code detection, and security alert and advisory controls.
Media Protection (MP): policies and procedures to ensure secure handling of media. Controls cover
access, labeling, storage, transport, sanitization, destruction, and disposal.
Incident Response (IR): policies and procedures pertaining to incident response training, testing,
handling, monitoring, reporting, and support services.
Awareness and Training (AT): policies and procedures to ensure that all information system users
are given appropriate security training relative to their usage of the system and that accurate training
records are maintained.
These operational controls are discussed in more detail in the sections to follow. ICS specific
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6.2.1 Personnel Security
The security controls that fall within the NIST SP 800-53 Personnel Security (PS) family provide policies
and procedures to reduce the risk of human error, theft, fraud, or other intentional or unintentional misuse
of information systems.
Supplemental guidance for the PS controls can be found in the following documents:
NIST SP 800-35 provides guidance on information technology security services [43].
NIST SP 800-73 provides guidance on interfaces for personal identity verification [48].
NIST SP 800-76 provides guidance on biometrics for personal identity verification [49].
Personnel security measures are meant to reduce the possibility and risk of human error, theft, fraud, or
other intentional or unintentional misuse of informational assets. There are three main aspects to
personnel security:
Hiring Policies. This includes pre-employment screening such as background checks, the interview
process, employment terms and conditions, complete job descriptions and detailing of duties, terms
and condition of employment, and legal rights and responsibilities of employees or contractors.
Organization Policies and Practices. These include security policies, information classification,
document and media maintenance and handling policies, user training, acceptable usage policies for
organization assets, periodic employee performance reviews, appropriate background checks, and any
other policies and actions that detail expected and required behavior of organization employees,
contractors, and visitors. Organization policies to be enforced should be written down and readily
available to all workers through an employee handbook, distributed as e-mail notices, located in a
centralized resource area, or posted directly at a worker’s area of responsibility.
Terms and Conditions of Employment. This category includes job and position responsibilities,
notification to employees of terminable offenses, disciplinary actions and punishments, and periodic
employee performance reviews.
Positions should be categorized with a risk designation and screening criteria, and individuals filling a
position should be screened against this criteria as well as complete an access agreement before being
granted access to an information system. Personnel should be screened for the critical positions
controlling and maintaining the ICS.
6.2.2 Physical and Environmental Protection
The security controls that fall within the NIST SP 800-53 Physical and Environmental Protection (PE)
family provide policy and procedures for all physical access to an information system including
designated entry/exit points, transmission media, and display media. These include controls for
monitoring physical access, maintaining logs, and handling visitors. This family also includes controls
for the deployment and management of emergency protection controls such as emergency shutdown of
the IT system, backup for power and lighting, controls for temperature and humidity, and protection
against fire and water damage.
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Supplemental guidance for the PE controls can be found in the following documents:
NIST SP 800-46 provides guidance on telecommuting and broadband communication security [50].
Physical security measures are designed to reduce the risk of accidental or deliberate loss or damage to
plant assets and the surrounding environment. The assets being safeguarded may be physical assets such
as tools and plant equipment, the environment, the surrounding community, and intellectual property,
including proprietary data such as process settings and customer information. The deployment of
physical security controls is often subject to environmental, safety, regulatory, legal, and other
requirements that must be identified and addressed specific to a given environment. The subject of
deploying physical security controls is vast and needs to be specific to the type of protection needed.
The physical protection of the cyber components and data associated with the ICS must be addressed as
part of the overall security of a plant. Security at many ICS facilities is closely tied to plant safety. A
primary goal is to keep people out of hazardous situations without preventing them from doing their job
or carrying out emergency procedures.
Gaining physical access to a control room or control system components often implies gaining logical
access to the process control system as well. Likewise, having logical access to systems such as main
servers and control room computers allows an adversary to exercise control over the physical process.
If computers are readily accessible, and they have removable media drives (e.g., floppy disks, compact
discs, external hard drives) or USB ports, the drives can be fitted with locks or removed from the
computers and USB ports disabled. Depending on security needs and risks, it might also be prudent to
disable or physically protect power buttons to prevent unauthorized use. For maximum security,
servers should be placed in locked areas and authentication mechanisms (such as keys) protected.
Also, the network devices on the ICS network, including switches, routers, network jacks, servers,
workstations, and controllers, should be located in a secured area that can only be accessed by
authorized personnel. The secured area should also be compatible with the environmental requirements
of the devices.
A defense-in-depth solution to physical security should include the following attributes:
Protection of Physical Locations. Classic physical security considerations typically refer to a
ringed architecture of layered security measures. Creating several physical barriers, both active and
passive, around buildings, facilities, rooms, equipment, or other informational assets, establishes
these physical security perimeters. Physical security controls meant to protect physical locations
include fences, anti-vehicle ditches, earthen mounds, walls, reinforced barricades, gates, or other
measures. Most organizations include this layered model by preventing access to the plant first by
the use of fences, guard shacks, gates, and locked doors.
Access Control. Access control systems should ensure that only authorized people have access to
controlled spaces. An access control system should be flexible. The need for access may be based
on time (day vs. night shift), level of training, employment status, work assignment, plant status,
and a myriad of other factors. A system must be able to verify that persons being granted access
are who they say they are (usually using something the person has, such as an access card or key;
something they know, such as a personal identification number (PIN); or something they are, using
a biometric device). Access control should be highly reliable, yet not interfere with the routine or
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emergency duties of plant personnel. Integration of access control into the process system allows a
view into not only security access, but also physical and personnel asset tracking, dramatically
accelerating response time in emergencies, helping to direct individuals to safe locations, and
improving overall productivity. Within an area, access to network and computer cabinets should be
limited to only those who have a need, such as network technicians and engineers, or computer
maintenance staff. Equipment cabinets should be locked and wiring should be neat and within
cabinets. Consider keeping all computers in secure racks and using peripheral extender technology
to connect human-machine interfaces to the racked computers.
Access Monitoring Systems. Access monitoring systems include still and video cameras, sensors,
and various types of identification systems. Examples of these systems include cameras that
monitor parking lots, convenience stores, or airline security. These devices do not specifically
prevent access to a particular location; rather, they store and record either the physical presence or
the lack of physical presence of individuals, vehicles, animals, or other physical entities. Adequate
lighting should be provided based on the type of access monitoring device deployed.
Access Limiting Systems. Access limiting systems may employ a combination of devices to
physically control or prevent access to protected resources. Access limiting systems include both
active and passive security devices such as fences, doors, safes, gates, and guards. They are often
coupled with identification and monitoring systems to provide role-based access for specific
individuals or groups of individuals.
People and Asset Tracking. Locating people and vehicles in a large installation is important for
safety reasons, and it is increasingly important for security reasons as well. Asset location
technologies can be used to track the movements of people and vehicles within the plant, to ensure
that they stay in authorized areas, to identify personnel needing assistance, and to support
emergency response.
Environmental Factors. In addressing the security needs of the system and data, it is important to
consider environmental factors. For example, if a site is dusty, systems should be placed in a
filtered environment. This is particularly important if the dust is likely to be conductive or
magnetic, as in the case of sites that process coal or iron. If vibration is likely to be a problem,
systems should be mounted on rubber bushings to prevent disk crashes and wiring connection
problems. In addition, the environments containing systems and media (e.g., backup tapes, floppy
disks) should have stable temperature and humidity. An alarm to the process control system should
be generated when environmental specifications such as temperature and humidity are exceeded.
Environmental Control Systems. Heating, ventilation, and air conditioning (HVAC) systems for
control rooms must support plant personnel during normal operation and emergency situations,
which could include the release of toxic substances. Fire systems must be carefully designed to
avoid causing more harm than good (e.g., to avoid mixing water with incompatible products).
HVAC and fire systems have significantly increased roles in security that arise from the
interdependence of process control and security. For example, fire prevention and HVAC systems
that support industrial control computers need to be protected against cyber incidents.
Power. Reliable power for the ICS is essential, so an uninterruptible power supply (UPS) should
be provided. If the site has an emergency generator, the UPS battery life may only need to be a
few seconds; however, if the site relies on external power, the UPS battery life may need to be
hours. It should be sized, at a minimum, so that the system can be shutdown safely.
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6.2.2.1 Control Center/Control Room
Providing physical security for the control center/control room is essential to reduce the potential of
many threats. Control centers/control rooms frequently have consoles continuously logged onto the
primary control server, where speed of response and continual view of the plant is of utmost
importance. These areas will often contain the servers themselves, other critical computer nodes, and
sometimes plant controllers. It is essential that access to these areas be limited to authorized users
only, using authentication methods such as smart or magnetic identity cards or biometric devices. In
extreme cases, it may be considered necessary to make the control center/control room blast-proof, or
to provide an offsite emergency control center/control room so that control can be maintained if the
primary control center/control room becomes uninhabitable.
6.2.2.2 Portable Devices
Computers and computerized devices used for ICS functions (such as PLC programming) should never
be allowed to leave the ICS area. Laptops, portable engineering workstations and handhelds (e.g., 375
HART communicator) should be tightly secured and should never be allowed to be used outside the
ICS network. Antivirus and patch management should be kept current.
6.2.2.3 Cabling
Cabling design and implementation for the control network should be addressed in the cyber security
plan. Unshielded twisted pair communications cable, while acceptable for the office environment, is
generally not suitable for the plant environment due to its susceptibility to interference from magnetic
fields, radio waves, temperature extremes, moisture, dust, and vibration. Industrial RJ-45 connectors
should be used in place of other types of twisted pair connectors to provide protection against moisture,
dust and vibration. Fiber-optic cable and coaxial cable are often better network cabling choices for the
control network because they are immune to many of the typical environmental conditions including
electrical and radio frequency interference found in an industrial control environment. Cable and
connectors should be color-coded and labeled so that the ICS and IT networks are clearly delineated
and the potential for an inadvertent cross-connect is reduced. Cable runs should be installed so that
access is minimized (i.e., limited to authorized personnel only) and equipment should be installed in
locked cabinets with adequate ventilation and air filtration.
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6.2.3 Contingency Planning
Contingency plans are designed to maintain or restore business operations, including computer
operations, possibly at an alternate location, in the event of emergencies, system failures, or disaster. The
security controls that fall within the NIST SP 800-53 Contingency Planning (CP) family provide policies
and procedures to implement a contingency plan by specifying roles and responsibilities, assigning
personnel and activities associated with restoring the information system after a disruption or failure.
Along with planning, controls also exist for contingency training, testing, and plan update, and for backup
information processing and storage sites.
Supplemental guidance for the CP controls can be found in the following documents:
NIST SP 800-34 provides guidance on contingency planning [51].
Contingency plans should cover the full range of failures or problems that could be caused by cyber
incidents. Contingency plans should include procedures for restoring systems from known valid
backups, separating systems from all non-essential interferences and connections that could permit
cyber security intrusions, and alternatives to achieve necessary interfaces and coordination. Employees
should be trained and familiar with the contents of the contingency plans. Contingency plans should be
periodically reviewed with employees responsible for restoration of the ICS, and tested to ensure that
they continue to meet their objectives. Organizations also have business continuity plans and disaster
recovery plans that are closely related to contingency plans. Because business continuity and disaster
recovery plans are particularly important for ICS, they are described in more detail in the sections to
follow.
.
6.2.3.1 Business Continuity Planning
Business continuity planning addresses the overall issue of maintaining or reestablishing production in the
case of an interruption. These interruptions may take the form of a natural disaster (e.g., hurricane,
tornado, earthquake, flood), an unintentional man-made event (e.g., accidental equipment damage, fire or
explosion, operator error), an intentional man-made event (e.g., attack by bomb, firearm or vandalism,
attacker or virus), or an equipment failure. From a potential outage perspective, this may involve typical
time spans of days, weeks, or months to recover from a natural disaster, or minutes or hours to recover
from a malware infection or a mechanical/electrical failure. Because there is often a separate discipline
that deals with reliability and electrical/mechanical maintenance, some organizations choose to define
business continuity in a way that excludes these sources of failure. Because business continuity also deals
primarily with the long-term implications of production outages, some organizations also choose to place
a minimum interruption limit on the risks to be considered. For the purposes of ICS cyber security, it is
recommended that neither of these constraints be made. Long-term outages (disaster recovery) and short-
term outages (operational recovery) should both be considered. Because some of these potential
interruptions involve man-made events, it is also important to work collaboratively with the physical
security organization to understand the relative risks of these events and the physical security
countermeasures that are in place to prevent them. It is also important for the physical security
organization to understand which areas of a production site house data acquisition and control systems
that might have higher-level risks.
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Before creating a business continuity plan (BCP) to deal with potential outages, it is important to specify
the recovery objectives for the various systems and subsystems involved based on typical business needs.
There are two distinct types of objectives: system recovery and data recovery. System recovery involves
the recovery of communication links and processing capabilities, and it is usually specified in terms of a
Recovery Time Objective (RTO). This is defined as the time required to recover the required
communication links and processing capabilities. Data recovery involves the recovery of data describing
production or product conditions in the past and is usually specified in terms of a Recovery Point
Objective (RPO). This is defined as the longest period of time for which an absence of data can be
tolerated.
Once the recovery objectives are defined, a list of potential interruptions should be created and the
recovery procedure developed and described. For most of the smaller scale interruptions, repair and
replace activities based on a critical spares inventory will prove adequate to meet the recovery objectives.
When this is not true, contingency plans need to be developed. Due to the potential cost and importance
of these contingency plans, they should be reviewed with the managers responsible for business
continuity planning to verify that they are justified. Once the recovery procedures are documented, a
schedule should be developed to test part or all of the recovery procedures. Particular attention must be
paid to the verification of backups of system configuration data and product or production data. Not only
should these be tested when they are produced, but the procedures followed for their storage should also
be reviewed periodically to verify that the backups are kept in environmental conditions that will not
render them unusable and that they are kept in a secure location, so they can be quickly obtained by
authorized individuals when needed.
6.2.3.2 Disaster Recovery Planning
A disaster recovery plan (DRP) is essential to continued availability of the ICS. The DRP should
include the following items:
Required response to events or conditions of varying duration and severity that would activate the
recovery plan
Procedures for operating the ICS in manual mode with all external electronic connections severed
until secure conditions can be restored
Roles and responsibilities of responders
Processes and procedures for the backup and secure storage of information
Complete and up-to-date logical network diagram
Personnel list for authorized physical and cyber access to the ICS
Communication procedure and list of personnel to contact in the case of an emergency including
ICS vendors, network administrators, ICS support personnel, etc
Current configuration information for all components
The plan should also indicate requirements for the timely replacement of components in the case of an
emergency. If possible, replacements for hard-to-obtain critical components should be kept in
inventory.
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The security plan should define a comprehensive backup and restore policy. In formulating this policy,
the following should be considered:
The speed at which data or the system must be restored. This requirement may justify the need for
a redundant system, spare offline computer, or valid file system backups.
The frequency at which critical data and configurations are changing. This will dictate the
frequency and completeness of backups.
The safe onsite and offsite storage of full and incremental backups
The safe storage of installation media, license keys, and configuration information
Identification of individuals responsible for performing, testing, storing, and restoring backups
6.2.4 Configuration Management
Configuration management policy and procedures are used to control modifications to hardware,
firmware, software, and documentation to ensure the information system is protected against improper
modifications prior to, during, and after system implementation. The security controls that fall within the
NIST SP 800-53 Configuration Management (CM) family provide policy and procedures for establishing
baseline controls for information systems. Controls are also specified for maintaining, monitoring, and
documenting configuration control changes. There should be restricted access to configuration settings,
and security settings of IT products should be set to the most restrictive mode consistent with ICS
operational requirements.
Supplemental guidance for the CM controls can be found in the following documents:
NIST SP 800-70 provides guidance on configuration settings for IT products [25].
A formal change management program should be established and procedures used to insure that all
modifications to an ICS network meet the same security requirements as the original components
identified in the asset evaluation and the associated risk assessment and mitigation plans. Risk
assessment should be performed on all changes to the ICS network that could affect security, including
configuration changes, the addition of network components, and installation of software. Changes to
policies and procedures may also be required. The current ICS network configuration must always be
known and documented.
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6.2.5 Maintenance
The security controls that fall within the NIST SP 800-53 Maintenance (MA) family provide policy and
procedure for performing routine and preventative maintenance on the components of an information
system. This includes the usage of maintenance tools (both local and remote) and management of
maintenance personnel.
Supplemental guidance for the MA controls can be found in the following documents:
NIST SP 800-63 provides guidance on electronic authentication for remote maintenance [52].
6.2.6 System and Information Integrity
Maintaining system and information integrity assures that sensitive data has not been modified or deleted
in an unauthorized and undetected manner. The security controls that fall within the NIST SP 800-53
System and Information Integrity (SI) family provide policies and procedures for identifying, reporting,
and correcting information system flaws. Controls exist for malicious code detection, spam and spyware
protection, and intrusion detection, although they may not be appropriate for all ICS applications. Also
provided are controls for receiving security alerts and advisories, and the verification of security functions
on the information system. In addition, there are controls within this family to detect and protect against
unauthorized changes to software and data, provide restrictions to data input and output, and check for the
accuracy, completeness, and validity of data as well as handle error conditions, although they may not be
appropriate for all ICS applications.
Supplemental guidance for the SI controls can be found in the following documents:
NIST SP 800-40 provides guidance on security patch installation [39].
NIST SP 800-94 provides guidance on Intrusion Detection and Prevention (IDP) Systems [54].
Controls exist for malicious code detection, spam and spyware protection, and intrusion detection,
although they may not be appropriate for all ICS applications. ICS specific recommendations and
guidance for these controls are included in Sections 6.2.6.1 through 6.2.6.3.
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6.2.6.1 Malicious Code Detection
Antivirus products evaluate files on a computer’s storage devices against an inventory of known malware
signature files. If one of the files on a computer matches the profile of a known virus, the virus is
removed through a disinfection process (e.g., quarantine, deletion) so it cannot infect other local files or
communicate across a network to infect other files. Antivirus software can be deployed on workstations,
servers, firewalls and handheld devices.
Antivirus tools only function effectively when installed, configured, running full-time, and maintained
properly against the state of known attack methods and payloads. While antivirus tools are common
security practice in IT computer systems, their use with ICS may require adopting special practices
including compatibility checks, change management issues, and performance impact metrics. These
special practices should be utilized whenever new signatures or new versions of antivirus software are
installed.
Major ICS vendors recommend and even support the use of particular antivirus tools. In some cases,
control system vendors may have performed regression testing across their product line for supported
versions of a particular antivirus tool and also provide associated installation and configuration
documentation. There is also an effort to develop a general set of guidelines and test procedures
focused on ICS performance impacts to fill the gaps where ICS and antivirus vendor guidance is not
available [55].
Generally:
Windows, Unix, Linux systems, etc. used as consoles, engineering workstations, data historians,
HMIs and general purpose SCADA and backup servers can be secured just like commercial IT
equipment: install push- or auto-updated antivirus and patch management software with updates
distributed via an antivirus server and patch management server located inside the process control
network and auto-updated from the IT network
Follow vendor recommendations on all other servers and computers (DCS, PLC, instruments) that
have time-dependent code, modified or extended the operating system or any other change that
makes it different from any standard PC that one could buy at an office supply or computer store.
Expect the vendor to make periodic maintenance releases that include security patches.
6.2.6.2 Intrusion Detection and Prevention
Intrusion detection systems (IDS) monitor events on a network, such as traffic patterns, or a system, such
as log entries or file accesses, so that they can identify an intruder breaking into or attempting to break
into a system [56]. IDS ensure that unusual activity such as new open ports, unusual traffic patterns, or
changes to critical operating system files is brought to the attention of the appropriate security personnel.
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The two most commonly used types of IDS are:
Network-Based IDS. These systems monitor network traffic and generate alarms when they identify
traffic that they deem to be an attack.
Host-Based IDS. This software monitors one or more types of characteristics of a system, such as
application log file entries, system configuration changes, and access to sensitive data on a system
and responds with an alarm or countermeasure when a user attempts to breach security.
An effective IDS deployment typically involves both host-based and network-based IDS. In the
current ICS environment, network-based IDS are most often deployed between the control network and
the corporate network in conjunction with a firewall; host-based IDS are most often deployed on the
computers that use general-purpose OSs or applications such as HMIs, SCADA servers, and
engineering workstations. Properly configured, an IDS can greatly enhance the security management
team’s ability to detect attacks entering or leaving the system, thereby improving security. They can
also potentially improve a control network’s efficiency by detecting non-essential traffic on the
network. However, even when IDS are implemented, security staff can primarily recognize individual
attacks, as opposed to organized patterns of attacks over time. Additionally, care should be given to
not confuse unusual ICS activity, such as during transient conditions, as an attack.
Current IDS and IPS products are effective in detecting and preventing well-known Internet attacks,
but until recently they have not addressed ICS protocol attacks. IDS and IPS vendors are beginning to
develop and incorporate attack signatures for various ICS protocols such as Modbus, DNP, and ICCP.
[57] Appendix D provides some additional information on emerging IDS capabilities.
6.2.6.3 Patch Management
Patches are additional pieces of code that have been developed to address specific problems or flaws in
existing software. Vulnerabilities are flaws that can be exploited, enabling unauthorized access to IT
systems or enabling users to have access to greater privileges than authorized.
A systematic approach to managing and using software patches can help organizations to improve the
overall security of their IT systems in a cost-effective way. Organizations that actively manage and use
software patches can reduce the chances that the vulnerabilities in their IT systems can be exploited; in
addition, they can save time and money that might be spent in responding to vulnerability-related
incidents.
NIST SP 800-40 Version 2 provides guidance for organizational security managers who are responsible
for designing and implementing security patch and vulnerability management programs and for testing
the effectiveness of the programs in reducing vulnerabilities. The guidance is also useful to system
administrators and operations personnel who are responsible for applying and testing patches and for
deploying solutions to vulnerability problems.
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Applying patches to OS components creates another situation where significant care should be
exercised in the ICS environment. Patches should be adequately tested (e.g., off-line on a comparable
ICS) to determine the acceptability of side effects. Regression testing is advised. It is not uncommon
for patches to have an adverse effect on other software. A patch may remove a vulnerability, but it can
also introduce a greater risk from a production or safety perspective. Patching the vulnerability may
also change the way the OS or application works with control applications, causing the control
application to lose some of its functionality. Another issue is that many ICS utilize older versions of
operating systems that are no longer supported by the vendor. Consequently, available patches may not
be applicable. Organizations should implement a systematic, accountable, and documented ICS patch
management process for managing exposure to vulnerabilities.
Once the decision is made to deploy a patch, there are other tools that automate this process from a
centralized server and with confirmation that the patch has been deployed correctly. Consider
separating the automated process for ICS patch management from the automated process for non-ICS
applications. Patching should be scheduled to occur during planned ICS outages.
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6.2.7 Media Protection
The security controls that fall within the NIST SP 800-53 Media Protection (MP) family provide policies
and procedures for limiting the access to media to authorized users. Controls also exist for labeling media
for distribution and handling requirements, as well as storage, transport, sanitization (removal of
information from digital media), destruction, and disposal of the media.
Supplemental guidance for the MP controls can be found in the following documents:
NIST SP 800-88 provides guidance on appropriate sanitization equipment, techniques, and
procedures [77].
Media assets include removable media and devices such as floppy disks, CDs, DVDs and USB
memory sticks, as well as printed reports and documents. Physical security controls should address
specific requirements for the safe and secure maintenance of these assets and provide specific guidance
for transporting, handling, and erasing or destroying these assets. Security requirements could include
safe storage from loss, fire, theft, unintentional distribution, or environmental damage. If an adversary
gains access to backup media associated with an ICS, it could provide valuable data for launching an
attack. Recovering an authentication file from the backups might allow an adversary to run password
cracking tools and extract usable passwords. In addition, the backups typically contain machine names,
IP addresses, software version numbers, usernames, and other data useful in planning an attack.
The use of any unauthorized CDs, DVDs, floppy disks, USB memory sticks, or similar removable
media on any node that is part of or connected to the ICS should not be permitted in order to prevent
the introduction of malware or the inadvertent loss or theft of data. Where the system components use
unmodified industry standard protocols, mechanized policy management software can be used to
enforce media protection policy.
6.2.8 Incident Response
An incident response plan is documentation of a predetermined set of instructions or procedures to detect,
respond to, and limit consequences of incidents against an organization’s information systems. Response
should be measured first and foremost against the “service being provided”, not just the system that was
compromised. If an incident is discovered, there should be a quick risk assessment performed to evaluate
the effect of both the attack and the options to respond. For example, one possible response option is to
physically isolate the system under attack. However, this may have such a dire impact on the service that
it is dismissed as not viable.
The security controls that fall within the NIST SP 800-53 Incident Response (IR) family provide policies
and procedures for incident response monitoring, handling, and reporting. The handling of a security
incident includes preparation, detection and analysis, containment, eradication, and recovery. Controls
also cover incident response training for personnel and testing the incident response capability for an
information system.
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Supplemental guidance for the IR controls can be found in the following documents:
NIST SP 800-61 provides guidance on incident handling and reporting [58].
NIST SP 800-83 provides guidance on malware incident prevention and handling [59].
Regardless of the steps taken to protect an ICS, it is always possible that it may be compromised by an
intentional or unintentional incident. The following symptoms can arise from normal network
problems, but when several symptoms start to appear, a pattern may indicate the ICS is under attack
and may be worth investigating further. If the adversary is skilled, it may not be very obvious that an
attack is underway.
The symptoms of an incident could include any of the following:
Unusually heavy network traffic
Out of disk space or significantly reduced free disk space
Unusually high CPU usage
Creation of new user accounts
Attempted or actual use of administrator-level accounts
Locked-out accounts
Account in-use when the user is not at work
Cleared log files
Full log files with unusually large number of events
Antivirus or IDS alerts
Disabled antivirus software and other security controls
Unexpected patch changes
Machines connecting to outside IP addresses
Requests for information about the system (social engineering attempts)
Unexpected changes in configuration settings
Unexpected system shutdown.
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To minimize the effects of these intrusions, it is necessary to plan a response. Incident response
planning defines procedures to be followed when an intrusion occurs. NIST SP 800-61, Computer
Security Incident Handling Guide, provides guidance on incident response planning, which might
include the following items:
Classification of Incidents. The various types of ICS incidents should be identified and classified
as to potential impact so that a proper response can be formulated for each potential incident.
Response Actions. There are several responses that can be taken in the event of an incident.
These range from doing nothing to full system shutdown (although full shutdown of an ICS is a
highly unlikely response). The response taken will depend on the type of incident and its effect on
the ICS system and the physical process being controlled. A written plan documenting the types of
incidents and the response to each type should be prepared. This will provide guidance during
times when there might be confusion or stress due to the incident. This plan should include step-
by-step actions to be taken by the various organizations. If there are reporting requirements, these
should be noted as well as where the report should be made and phone numbers to reduce reporting
confusion.
Recovery Actions. The results of the intrusion could be minor, or the intrusion could cause many
problems in the ICS. Risk analysis should be conducted to determine the sensitivity of the physical
system being controlled to failure modes in the ICS. In each case, step-by-step recovery actions
should be documented so that the system can be returned to normal operations as quickly and
safely as possible.
During the preparation of the incident response plan, input should be obtained from the various
stakeholders including operations, engineering, IT, system support vendors, management, organized
labor, legal, and safety. These stakeholders should also review and approve the plan.
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6.2.9 Awareness and Training
The security controls that fall within the NIST SP 800-53 Awareness and Training (AT) family provide
policy and procedures for ensuring that all users of an information system are provided basic information
system security awareness and training materials before authorization to access the system is granted.
Personnel training must be monitored and documented.
Supplemental guidance for the AT controls can be found in the following documents:
NIST SP 800-16 provides guidance on security training requirements
NIST SP 800-50 provides guidance on security awareness training [60].
For the ICS environment, this must include control system-specific information security awareness and
training for specific ICS applications. In addition, an organization must identify, document, and train
all personnel having significant ICS roles and responsibilities. Awareness and training must cover the
physical process being controlled as well as the ICS.
Security awareness is a critical part of ICS incident prevention, particularly when it comes to social
engineering threats. Social engineering is a technique used to manipulate individuals into giving away
private information, such as passwords. This information can then be used to compromise otherwise
secure systems.
Implementing an ICS security program may bring changes to the way in which personnel access
computer programs, applications, and the computer desktop itself. Organizations should design
effective training programs and communication vehicles to help employees understand why new access
and control methods are required, ideas they can use to reduce risks, and the impact on the organization
if control methods are not incorporated. Training programs also demonstrate management’s
commitment to, and the value of, a cyber security program. Feedback from staff exposed to this type
of training can be a valuable source of input for refining the charter and scope of the security program.
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6.3 Technical Controls
Technical controls are the security countermeasures for an ICS that are primarily implemented and
executed by the system through mechanisms contained in the hardware, software, or firmware
components of the system. As discussed in detail in the following subsections, NIST SP 800-53 defines
four families of controls within the Technical controls class:
Identification and Authentication (IA): the process of verifying the identity of a user, process, or
device, through the use of specific credentials (e.g., passwords, tokens, biometrics), as a prerequisite
for granting access to resources in an IT system.
Access Control (AC): the process of granting or denying specific requests for obtaining and using
information and related information processing services for physical access to areas within the
information system environment.
Audit and Accountability (AU): independent review and examination of records and activities to
assess the adequacy of system controls, to ensure compliance with established policies and
operational procedures, and to recommend necessary changes in controls, policies, or procedures.
System and Communications Protection (SC): mechanisms for protecting both system and data
transmission components.
These technical controls are discussed in more detail in the sections to follow. ICS specific
Additional ICS specific guidance pertaining to technical controls can be found in ISA TR99.00.01 [33]
and the EPRI report: Supervisory Control and Data Acquisition (SCADA) Systems Security Guide [61].
6.3.1 Identification and Authentication
Authentication describes the process of positively identifying potential network users, hosts, applications,
services, and resources using a combination of identification factors or credentials. The result of this
authentication process then becomes the basis for permitting or denying further actions (e.g., when an
automatic teller machine asks for a PIN). Based on the authentication determination, the system may or
may not allow the potential user access to its resources. Authorization is the process of determining who
and what should be allowed to have access to a particular resource; access control is the mechanism for
enforcing authorization. Access control is described in Section 6.3.2.
There are several possible factors for determining the authenticity of a person, device, or system,
including something you know, something you have or something you are. For example, authentication
could be based on something known (e.g., PIN number or password), something possessed (e.g., key,
dongle, smart card), something you are such as a biological characteristic (e.g., fingerprint, retinal
signature), a location (e.g., Global Positioning System [GPS] location access), the time a request is made,
or a combination of these attributes. In general, the more factors that are used in the authentication
process, the more robust the process will be. When two or more factors are used, the process is known
generically as multi-factor authentication.
The security controls that fall within the NIST SP 800-53 Identification and Authentication (IA) family
provide policy and guidance for the identification and authentication of users of and devices within the
information system. These include controls to manage identifiers and authenticators within each
technology used (e.g., tokens, certificates, biometrics, passwords, key cards).
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Supplemental guidance for the IA controls can be found in the following documents:
NIST SP 800-63 provides guidance on remote electronic authentication [52].
Computer systems in ICS environments typically rely on traditional passwords for authentication.
Control system suppliers often supply systems with default passwords. These passwords are factory set
and are often easy to guess or are changed infrequently, which creates additional security risks. Also,
protocols currently used in ICS environments generally have inadequate or no network service
authentication. There are now several forms of authentication available in addition to traditional
password techniques being used with ICS. Some of these, including password authentication, are
presented in the following sections with discussions regarding their use with ICS.
6.3.1.1 Password Authentication
Password authentication technologies determine authenticity based on testing for something the device or
human requesting access should know, such as a PIN number or password. Password authentication
schemes are thought of as the simplest and most common forms of authentication.
Password vulnerabilities can be reduced by using an active password checker that prohibits weak,
recently used, or commonly used passwords. Another weakness is the ease of third-party eavesdropping.
Passwords typed at a keypad or keyboard are easily observed or recorded, especially in areas where
adversaries could plant tiny wireless cameras or keystroke loggers. Network service authentication often
transmits passwords as plaintext (unencrypted), allowing any network capture tool to expose the
passwords.
One problem with passwords unique to the ICS environment is that a user’s ability to recall and enter a
password may be impacted by the stress of the moment. During a major crisis when human
intervention is critically required to control the process, an operator may panic and have difficulty
remembering or entering the password and either be locked out completely or be delayed in responding
to the event. Biometric identifiers may have similar drawbacks. Organizations should carefully
consider the security needs and the potential ramifications of the use of authentication mechanisms on
these critical systems. In situations where the ICS cannot support, or the organization determines it is
not advisable (e.g., performance, safety, or reliability are adversely impacted), to implement
authentication mechanisms in an ICS, the organization uses compensating controls, such as rigorous
physical security controls to provide an equivalent security capability or level of protection for the ICS.
This guidance also applies to the use of session lock and session termination in an ICS.
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Some ICS operating systems make setting secure passwords difficult, as the password size is very small
and the system allows only group passwords at each level of access, not individual passwords. Some
industrial (and Internet) protocols transmit passwords in plaintext, making them susceptible to
interception. In cases where this practice cannot be avoided, it is important that users have different
(and unrelated) passwords for use with encrypted and non-encrypted protocols.
The following are general recommendations and considerations with regards to the use of passwords.
The length, strength, and complexity of passwords should balance security and operational ease of
access within the capabilities of the software and underlying OS.
Passwords should have appropriate length and complexity for the required security. In particular,
they should not be able to be found in a dictionary or contain predictable sequences of numbers or
letters.
Passwords should be used with care on operator interface devices such as control consoles on
critical processes. Using passwords on these consoles could introduce potential safety issues if
operators are locked out or delayed access during critical events. Physical security should
supplement operator control consoles when password protection is not feasible.
The keeper of master passwords should be a trusted employee, available during emergencies. Any
copies of the master passwords must be stored in a very secure location with limited access.
The passwords of privileged users (such as network technicians, electrical or electronics
technicians and management, and network designers/operators) should be most secure and be
changed frequently. Authority to change master passwords should be limited to trusted employees.
A password audit record, especially for master passwords, should be maintained separately from
the control system.
In environments with a high risk of interception or intrusion (such as remote operator interfaces in
a facility that lacks local physical security access controls), organizations should consider
supplementing password authentication with other forms of authentication such as
challenge/response or multi-factor authentication using biometric or physical tokens.
For user authentication purposes, password use is common and generally acceptable for users
logging directly into a local device or computer. Passwords should not be sent across any network
unless protected by some form of FIPS-approved encryption or salted cryptographic hash
specifically designed to prevent replay attacks. It is assumed that the device used to enter a
password is connected to the network in a secure manner.
For network service authentication purposes, passwords should be avoided if possible. There are
more secure alternatives available, such as challenge/response or public key authentication.
6.3.1.2 Challenge/response Authentication
Challenge/response authentication requires that both the service requester and service provider know a
“secret” code in advance. When service is requested, the service provider sends a random number or
string as a challenge to the service requester. The service requester uses the secret code to generate a
unique response for the service provider. If the response is as expected, it proves that the service
requester has access to the “secret” without ever exposing the secret on the network.
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Challenge/response authentication addresses the security vulnerabilities of traditional password
authentication. When passwords (hashed or plain) are sent across a network, a portion of the actual
“secret” itself is being sent. Authentication is performed by giving the secret to the remote device.
6.3.1.3 Physical Token Authentication
Physical or token authentication is similar to password authentication, except that these technologies
determine authenticity by testing for secret code or key produced by a device or token the person
requesting access has in their possession, such as security tokens or smart cards. Increasingly, private
keys are being embedded in physical devices such as USB dongles. Some tokens support single-factor
authentication only, so that simply having possession of the token is sufficient to be authenticated. Others
support multi-factor authentication that requires knowledge of a PIN or password in addition to
possessing the token.
The primary vulnerability that token authentication addresses is easily duplicating a secret code or sharing
it with others. It eliminates the all-too-common scenario of a password to a “secure” system being left on
the wall next to a PC or operator station. The security token cannot be duplicated without special access
to equipment and supplies. A second benefit is that the secret within a physical token can be very large,
physically secure, and randomly generated. Because it is embedded in metal or silicon, it does not have
the same risks that manually entered passwords do. If a security token is lost or stolen, the authorized
user loses access, unlike traditional passwords that can be lost or stolen without notice.
Common forms of physical/token authentication include:
Traditional physical lock and keys
Security cards (e.g., magnetic, smart chip, optical coding)
Radio frequency devices in the form of cards, key fobs, or mounted tags
Dongles with secure encryption keys that attach to the USB, serial, or parallel ports of computers
One-time authentication code generators (e.g., key fobs)
For single-factor authentication, the largest weakness is that physically holding the token means access is
granted (e.g., anyone finding a set of lost keys now has access to whatever they open). Physical/token
authentication is more secure when combined with a second form of authentication, such as a memorized
PIN used along with the token.
Multi-factor authentication is an accepted good practice for access to ICS applications from outside the
ICS firewall.
Physical/token authentication has the potential for a strong role in ICS environments. An access card
or other token can be an effective form of authentication for computer access, as long as the computer
is in a secure area (e.g., once the operator has gained access to the room with appropriate secondary
authentication, the card alone can be used to enable control actions).
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6.3.1.4 Biometric Authentication
Biometric authentication technologies determine authenticity by determining presumably unique
biological characteristics of the human requesting access. Usable biometric features include finger
minutiae, facial geometry, retinal and iris signatures, voice patterns, typing patterns, and hand geometry.
Like physical tokens and smart cards, biometric authentication enhances software-only solutions, such as
password authentication, by offering an additional authentication factor and removing the human element
in memorizing complex secrets. In addition, because biometric characteristics are unique to a given
individual, biometric authentication addresses the issues of lost or stolen physical tokens and smart cards.
Noted issues with biometric authentication include:
Distinguishing a real object from a fake (e.g., how to distinguish a real human finger from a silicon-
rubber cast of one or a real human voice from a recorded one).
Generating type-I and type-II errors (the probability of rejecting a valid biometric image, and the
probability of accepting an invalid biometric image, respectively). Biometric authentication devices
should be configured to the lowest crossover between these two probabilities, also known as the
crossover error rate.
Handling environmental factors such as temperature and humidity to which some biometric devices
are sensitive.
Addressing industrial applications where employees may have on safety glasses and/or gloves and
industrial chemicals may impact biometric scanners.
Retraining biometric scanners that occasionally “drift” over time. Human biometric traits may also
shift over time, necessitating periodic scanner retraining.
Requiring face-to-face technical support and verification for device training, unlike a password that
can be given over a phone or an access card that can be handed out by a receptionist.
Denying needed access to the control system because of a temporary inability of the sensing device to
acknowledge a legitimate user.
Being socially acceptable. Users consider some biometric authentication devices more acceptable
than others. For example, retinal scans may be considered very low on the scale of acceptability,
while thumb print scanners may be considered high on the scale of acceptability. Users of biometric
authentication devices will need to take social acceptability for their target group into consideration
when selecting among various biometric authentication technologies.
Biometric devices make a useful secondary check versus other forms of authentication that can become
lost or borrowed. Using biometric authentication in combination with token-based access control or
badge-operated employee time clocks increases the security level. A possible application is in a control
room that is environmentally controlled and physically secured [33].
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6.3.2 Access Control
The security controls that fall within the NIST SP 800-53 Access Control (AC) family provide policies
and procedures for specifying the use of system resources by only authorized users, programs, processes,
or other systems. This family specifies controls for managing information system accounts, including
establishment, activating, modifying, reviewing, disabling, and removing accounts. Controls cover access
and flow enforcement issues such as separation of duties, least privilege, unsuccessful login attempts,
system use notification, previous logon notification, concurrent session control, session lock, and session
termination. There are also controls to address the use of portable and remote devices and personally
owned information systems to access the information system as well as the use of remote access
capabilities and the implementation of wireless technologies.
Access can take several forms, including viewing, using, and altering specific data or device functions.
Supplemental guidance for the AC controls can be found in the following documents:
NIST SP 800-48 provides guidance on wireless network security with particular emphasis on the
IEEE 802.11b and Bluetooth standards [62].
NIST SP 800-97 provides guidance on IEEE 802.11i wireless network security [63].
FIPS 201 requirements for the personal identity verification of federal employees and contractors
[64].
NIST SP 800-96 provides guidance on PIV card to reader interoperability [65].
NIST SP 800-78 provides guidance on cryptographic algorithms and key sizes for personal identity
verification [66].
If the new federal Personal Identity Verification (PIV) is used as an identification token, the access
control system should conform to the requirements of FIPS 201 and NIST SP 800-73 and employ either
cryptographic verification or biometric verification. When token-based access control employs
cryptographic verification, the access control system should conform to the requirements of NIST SP
800-78. When token-based access control employs biometric verification, the access control system
should conform to the requirements of NIST SP 800-76.
Access control technologies are filter and blocking technologies designed to direct and regulate the flow
of information between devices or systems once authorization has been determined. The following
sections present several access control technologies and their use with ICS.
6.3.2.1 Role-based Access Control (RBAC)
RBAC is a technology that has the potential to reduce the complexity and cost of security administration
in networks with large numbers of intelligent devices. Under RBAC, security administration is simplified
through the use of roles, hierarchies, and constraints to organize user access levels. RBAC reduces costs
within an organization because it accepts that employees change roles and responsibilities more
frequently than the duties within roles and responsibilities.
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RBAC can be used to provide a uniform means to manage access to ICS devices while reducing the
cost of maintaining individual device access levels and minimizing errors. RBAC should be used to
restrict ICS user privileges to only those that are required to perform each person’s job (i.e.,
configuring each role based on the principle of least privilege).
6.3.2.2 Web Servers
Web and Internet technologies are being added to a wide variety of ICS products because they make
information more accessible and products more user-friendly and easier to configure remotely. However,
they may also add cyber risks and create new security vulnerabilities that need to be addressed.
SCADA and historian software vendors typically provide Web servers as a product option so that users
outside the control room can access ICS information. In many cases, software components such as
ActiveX controls or Java applets must be installed or downloaded onto each client machine accessing
the Web server. Some products, such as PLCs and other control devices, are available with embedded
Web, FTP, and e-mail servers to make them easier to configure remotely and allow them to generate e-
mail notifications and reports when certain conditions occur. When feasible, use HTTPS rather than
HTTP, use SFTP or SCP rather than FTP, block inbound FTP and e-mail traffic, etc.
6.3.2.3 Virtual Local Area Network (VLAN)
VLANs divide physical networks into smaller logical networks to increase performance, improve
manageability, and simplify network design. VLANs are achieved through configuration of Ethernet
switches. Each VLAN consists of a single broadcast domain that isolates traffic from other VLANs. Just
as replacing hubs with switches reduces collisions, using VLANs limits the broadcast traffic, as well as
allowing logical subnets to span multiple physical locations. There are two categories of VLANs:
Static, often referred to as port-based, where switch ports are assigned to a VLAN so that it is
transparent to the end user
Dynamic, where an end device negotiates VLAN characteristics with the switch or determines the
VLAN based on the IP or hardware addresses.
Although more than one IP subnet may coexist on the same VLAN, the general recommendation is to use
a one-to-one relationship between subnets and VLANs. This practice requires the use of a router or
multi-layer switch to join multiple VLANs. Many routers and firewalls support tagged frames so that a
single physical interface can be used to route between multiple logical networks.
VLANs are not typically deployed to address host or network vulnerabilities in the way that firewalls or
IDS are deployed. However, when properly configured, VLANs do allow switches to enforce security
policies and segregate traffic at the Ethernet layer. Properly segmented networks can also mitigate the
risks of broadcast storms that may result from port scanning or worm activity.
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Switches have been susceptible to attacks such as MAC spoofing, table overflows, and attacks against the
spanning tree protocols, depending on the device and its configuration. VLAN hopping, the ability for an
attack to inject frames to unauthorized ports, has been demonstrated using switch spoofing or double-
encapsulated frames. These attacks cannot be conducted remotely and require local physical access to the
switch. A variety of features such as MAC address filtering, port-based authentication using IEEE
802.1x, and specific vendor recommended practices can be used to mitigate these attacks, depending on
the device and implementation.
VLANs have been effectively deployed in ICS networks, with each automation cell assigned to a single
VLAN to limit unnecessary traffic flooding and allow network devices on the same VLAN to span
multiple switches [33].
6.3.2.4 Dial-up Modems
ICS systems have stringent reliability and availability requirements. When there is a need to troubleshoot
and repair, the technical resources may not be physically located at the control room or facility.
Therefore, ICS often use modems to enable vendors, system integrators, or control engineers maintaining
the system to dial in and diagnose, repair, configure, and perform maintenance on the network or
component. While this allows easy access for authorized personnel, if the dial-up modems are not
properly secured, they can also provide backdoor entries for unauthorized use.
Dial-up often uses remote control software that gives the remote user powerful (administrative or root)
access to the target system. Such software usually has security options that should be carefully reviewed
and configured.
Consider using callback systems when dial-up modems are installed in an ICS. This ensures that a
dialer is an authorized user by having the modem establish the working connection based on the
dialer’s information and a callback number stored in the ICS approved authorized user list.
Ensure that default passwords have been changed and strong passwords are in place for each
modem.
Physically identify modems in use to the control room operators.
Configure remote control software to use unique user names and passwords, strong authentication,
encryption if determined appropriate, and audit logs. Use of this software by remote users should
be monitored on an almost real-time frequency.
If feasible, disconnect modems when not in use or consider automating this disconnection process
by having modems disconnect after being on for a given amount of time. It should be noted that
sometimes modem connections are part of the legal support service agreement with the vendor
(e.g., 24x7 support with 15 minute response time). Personnel should be aware that
disconnecting/removing the modems may require that contracts be renegotiated.
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6.3.2.5 Wireless
The use of wireless within an ICS is a risk-based decision that has to be determined by the organization.
Generally, wireless LANs should only be deployed where health, safety, environmental, and financial
implications are low. NIST SP 800-48 and SP 800-97 provide guidance on wireless network security.
Wireless LANs
Prior to installation, a wireless survey should be performed to determine antenna location and
strength to minimize exposure of the wireless network. The survey should take into account the
fact that attackers can use powerful directional antennas, which extend the effective range of a
wireless LAN beyond the expected standard range. Faraday cages and other methods are also
available to minimize exposure of the wireless network outside of the designated areas.
Wireless users’ access should utilize IEEE 802.1x authentication using a secure authentication
protocol (e.g., Extensible Authentication Protocol [EAP] with TLS [EAP-TLS]) that authenticates
users via a user certificates or a Remote Authentication Dial In User Service (RADIUS) server.
The wireless access points and data servers for wireless worker devices should be located on an
isolated network with documented and minimal (single if possible) connections to the ICS network.
Wireless access points should be configured to have a unique service set identifier (SSID), disable
SSID broadcast, and enable MAC filtering at a minimum.
Wireless devices, if being utilized in a Microsoft Windows ICS network, should be configured into
a separate organizational unit of the Windows domain.
Wireless device communications should be encrypted and integrity-protected. The encryption
must not degrade the operational performance of the end device. Encryption at OSI Layer 2
should be considered, rather than at Layer 3 to reduce encryption latency. The use of hardware
accelerators to perform cryptographic functions should also be considered.
For mesh networks, consider the use of broadcast key versus public key management implemented at
OSI Layer 2 to maximize performance. Asymmetric cryptography should be used to perform
administrative functions, and symmetric encryption should be used to secure each data stream as well
as network control traffic. An adaptive routing protocol should be considered if the devices are to be
used for wireless mobility. The convergence time of the network should be as fast as possible
supporting rapid network recovery in the event of a failure or power loss. The use of a mesh network
may provide fault tolerance thru alternate route selection and pre-emptive fail-over of the network.
Wireless field networks
The ISA10020
Committee is working to establish standards, recommended practices, technical reports,
and related information that will define procedures for implementing wireless systems in the
automation and control environment with a focus on the field level (e.g., IEEE 802.15.4). Guidance is
directed towards those responsible for the complete life cycle including the designing, implementing,
on-going maintenance, scalability or managing industrial automation and control systems, and applies
to users, system integrators, practitioners, and control systems manufacturers and vendors.
20
Additional information on ISA100 at: http://www.isa.org/isa100
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6.3.3 Audit and Accountability
An audit is an independent review and examination of records and activities to assess the adequacy of
system controls, to ensure compliance with established policies and operational procedures, and to
recommend necessary changes in controls, policies, or procedures. The security controls that fall within
the NIST SP 800-53 Audit and Accountability (AU) family provide policies and procedures for
generating audit records, their content, capacity, and retention requirements. The controls also provide
safeguards to react to problems such as an audit failure or audit log capacity being reached. Audit data
should be protected from modification and be designed with non-repudiation capability.
Supplemental guidance for the AU controls can be found in the following documents:
NIST SP 800-61 provides guidance on computer security incident handling and audit log retention
[58].
NIST SP 800-92 provides guidance on log management (including audit logs) [67]
It is necessary to determine that the system is performing as intended. Periodic audits of the ICS
should be performed to validate the following items:
The security controls present during system validation testing (e.g., factory acceptance testing and
site acceptance testing) are still installed and operating correctly in the production system.
The production system is free from security compromises and provides information on the nature
and extent of compromises as feasible, should they occur.
The management of change program is being rigorously followed with an audit trail of reviews and
approvals for all changes.
The results from each periodic audit should be expressed in the form of performance against a set of
predefined and appropriate metrics to display security performance and security trends. Security
performance metrics should be sent to the appropriate stakeholders, along with a view of security
performance trends.
Traditionally, the primary basis for audit in IT systems has been recordkeeping. Using appropriate
tools within an ICS environment requires extensive knowledge from an IT professional familiar with
the ICS, critical production and safety implications for the facility. Many of the process control
devices that are integrated into the ICS have been installed for many years and do not have the
capability to provide the audit records described in this section. Therefore, the applicability of these
more modern tools for auditing system and network activity is dependent upon the capabilities of the
components in the ICS.
The critical tasks in managing a network in an ICS environment are ensuring reliability and availability
to support safe and efficient operation. In regulated industries, regulatory compliance can add
complexity to security and authentication management, registry and installation integrity management,
and all functions that can augment an installation and operational qualification exercise. Diligent use
of auditing and log management tools can provide valuable assistance in maintaining and proving the
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integrity of the ICS from installation through the system life cycle. The value of these tools in this
environment can be calculated by the effort required to re-qualify or otherwise retest the ICS where the
integrity due to attack, accident, or error is in question. The system should provide reliable,
synchronized time stamps in support of the audit tools.
Monitoring of sensors, logs, IDS, antivirus, patch management, policy management software, and other
security mechanisms should be done on a real-time basis where feasible. A first-line monitoring
service would receive alarms, do rapid initial problem determination and take action to alert
appropriate facility personnel to intervene.
System auditing utilities should be incorporated into new and existing ICS projects. These auditing
utilities should be tested (e.g., off-line on a comparable ICS) before being deployed on an operational
ICS. These tools can provide tangible records of evidence and system integrity. Additionally, active
log management utilities may actually flag an attack or event in progress and provide location and
tracing information to help respond to the incident [33].
There should be a method for tracing all console activities to a user, either manually (e.g., control room
sign in) or automatic (e.g., login at the application and/or OS layer). Policies and procedures for what
is logged, how the logs are stored (or printed), how they are protected, who has access to the logs and
how/when are they reviewed should be developed. These policies and procedures will vary with the
ICS application and platform. Legacy systems typically employ printer loggers, which are reviewed by
administrative, operational, and security staff. Logs maintained by the ICS application may be stored
at various locations and may or may not be encrypted.
6.3.4 System and Communications Protection
The security controls that fall within the NIST SP 800-53 System and Communications Protection (SC)
family provide policy and procedures for protecting systems and data communications components.
Supplemental guidance for the SC controls can be found in the following documents:
NIST SP 800-28 provides guidance on active content and mobile code [68].
NIST SP 800-52 provides guidance on Transport Layer Security (TLS) Implementations [69]
NIST SP 800-56 provides guidance on cryptographic key establishment [70].
NIST SP 800-57 provides guidance on cryptographic key management [71].
NIST SP 800-58 provides guidance on security considerations for VoIP technologies [72].
NIST SP 800-77 provides guidance on IPsec VPNs [73].
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6.3.4.1 Encryption
Encryption is the cryptographic transformation of data (called plaintext) into a form (called ciphertext)
that conceals the data’s original meaning to prevent it from being known or used. If the transformation is
reversible, the corresponding reversal process is called decryption, which is a transformation that restores
encrypted data to its original state [74].
Before deploying encryption, first determine if encryption is an appropriate solution for the specific
ICS application, because authentication and integrity are generally the key security issues for ICS
applications. Other cryptographic solutions such as cryptographic hashes should also be considered.
The use of encryption within an ICS environment could introduce communications latency due to the
additional time and computing resources required to encrypt, decrypt, and authenticate each message.
For ICS, any latency induced from the use of encryption, or any other security technique, must not
degrade the operational performance of the end device or system. Encryption at OSI Layer 2 should be
considered, rather than at Layer 3 to reduce encryption latency.
In addition, encrypted messages are often larger than unencrypted messages due to one or more of the
following:
Additional checksums to reduce errors
Protocols to control the cryptography
Padding (for block ciphers)
Authentication procedures
Other required cryptographic processes.
Cryptography also introduces key management issues. Sound security policies require periodic key
changes. This process becomes more difficult as the geographic size of the ICS increases, with
extensive SCADA systems being the most severe example. Because site visits to change keys can be
costly and slow, it is useful to be able to change keys remotely.
If cryptography is selected, the most effective safeguard is to use a complete cryptographic system
approved by the NIST/ Communications Security Establishment (CSE) Cryptographic Module
Validation Program (CMVP)21
. Within this program standards are maintained to ensure that
cryptographic systems were studied carefully for weaknesses by a wide range of experts, rather than
being developed by a few engineers in a single organization. At a minimum, certification makes it
probable that:
Some method (such as counter mode) will be used to ensure that the same message does not
generate the same value each time
ICS messages are protected against replay and forging
Key management is secure throughout the life cycle of the key
21
Information on the CMVP can be found on the CMVP web site http://csrc.nist.gov/cryptval/cmvp.htm
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The system is using an effective random number generator
The entire system has been implemented securely.
Even then, the technology is only effective if it is an integral part of an effectively enforced information
security policy. American Gas Association (AGA) report 12-1 [5] contains an example of such a
security policy. While it is directed toward a natural gas SCADA system, many of its policy
recommendations could apply to any ICS.
For an ICS, encryption can be deployed as part of a comprehensive, enforced security policy.
Organizations should select cryptographic protection based on a risk assessment and the identified
value of the information being protected and ICS operating constraints. Specifically, a cryptographic
key should be long enough so that guessing it or determining it through analysis takes more effort,
time, and cost than the value of the protected asset.
The encryption hardware should be protected from physical tampering and uncontrolled electronic
connections. Assuming cryptography is the appropriate solution, organizations should select
cryptographic protection with remote key management if the units being protected are so numerous or
geographically dispersed that changing keys is difficult or expensive. [33]
6.3.4.2 Virtual Private Network (VPN)
One method of encrypting communication data is through a VPN, which is a private network that
operates as an overlay on a public infrastructure, so that the private network can function across a public
network. The most common types of VPN technologies implemented today are:
Internet Protocol Security (IPsec). IPsec is a set of standards defined by IETF to govern the secure
communications of data across public networks at the IP layer. IPsec is included in many current
operating systems. The intent of the standards is to guarantee interoperability across vendor
platforms; however, the reality is that the determination of interoperability of multi-vendor
implementations depends on specific implementation testing conducted by the end-user organization.
IPsec supports two encryption modes: transport and tunnel. Transport mode encrypts only the data
portion (payload) of each packet, but leaves the header untouched. The more secure tunnel mode
adds a new header to each packet and encrypts both the original header and the payload. On the
receiving side, an IPsec-compliant device decrypts each packet. The protocol has been continually
enhanced to address specific requirements, such as extensions to the protocol to address individual
user authentication and NAT device transversal. These extensions are typically vendor-specific and
can lead to interoperability issues primarily in host-to-security gateway environments. NIST SP 800-
77 provides guidance on IPsec VPNs.
Secure Sockets Layer (SSL). SSL provides a secure channel between two machines that encrypts
the contents of each packet. The IETF made slight modifications to the SSL version 3 protocol and
created a new protocol called Transport Layer Security (TLS). The terms “SSL” and “TLS” are often
used interchangeably, and this document generically uses the SSL terminology. SSL is most often
recognized for securing HTTP traffic; this protocol implementation is known as HTTP Secure
(HTTPS). However, SSL is not limited to HTTP traffic; it can be used to secure many different
application layer programs. SSL-based VPN products have gained acceptance because of the market
for “clientless” VPN products. These products use standard Web browsers as clients, which have
built-in SSL support. The “clientless” term means that there is no need to install or configure third-
6-34

6-35
party VPN “client” software on users’ systems. NIST SP 800-52 provides guidance on SSL
configuration.
Secure Shell (SSH). SSH is a command interface and protocol for securely gaining access to a
remote computer. It is widely used by network administrators to remotely control Web servers and
other types of servers. The latest version, SSH2, is a proposed set of standards from the IETF.
Typically, SSH is deployed as a secure alternative to a telnet application. SSH is included in most
UNIX distributions, and is typically added to other platforms through a third-party package.
VPNs are most often used in the ICS environment to provide secure access from an untrusted network
to the ICS control network. Untrusted networks can range from the Internet to the corporate LAN.
Properly configured, VPNs can greatly restrict access to and from control system host computers and
controllers, thereby improving security. They can also potentially improve control network
responsiveness by removing unauthorized non-essential traffic from the intermediary network. VPN
devices used to protect control systems should be thoroughly tested to verify that the VPN technology
is compatible with the application and implementation of the VPN devices does not unacceptably affect
network traffic characteristics [33].

Appendix A—Acronyms and Abbreviations
Selected acronyms and abbreviations used in the Guide to Industrial Control Systems (ICS) Security are
defined below.
AC Alternating Current
ACL Access Control List
AGA American Gas Association
API American Petroleum Institute
ARP Address Resolution Protocol
BCP Business Continuity Plan
CIDX Chemical Industry Data Exchange
CIGRE International Council on Large Electric Systems
CIP Critical Infrastructure Protection
CMVP Cryptographic Module Validation Program
COTS Commercial Off-the-Shelf
CPNI Centre for the Protection of National Infrastructure
CPU Central Processing Unit
CSE Communications Security Establishment
CSRC Computer Security Resource Center
CSSC Control System Security Center
CVE Common Vulnerabilities and Exposures
DCOM Distributed Component Object Model
DCS Distributed Control System(s)
DETL Distributed Energy Technology Laboratory
DHS Department of Homeland Security
DMZ Demilitarized Zone
DNP Distributed Network Protocol
DNS Domain Name System
DOE Department of Energy
DoS Denial of Service
DRP Disaster Recovery Plan
EAP Extensible Authentication Protocol
EMS Energy Management System
EPRI Electric Power Research Institute
ERP Enterprise Resource Planning
FIPS Federal Information Processing Standards
FISMA Federal Information Security Management Act
FTP File Transfer Protocol
GAO Government Accountability Office
GPS Global Positioning System
HMI Human-Machine Interface
HSPD Homeland Security Presidential Directive
A-1

HTTP Hypertext Transfer Protocol
HTTPS Hypertext Transfer Protocol Secure
HVAC Heating, Ventilation, and Air Conditioning
I/O Input/Output
I3P Institute for Information Infrastructure Protection
IAONA Industrial Automation Open Networking Association
ICMP Internet Control Message Protocol
ICS Industrial Control System(s)
IDS Intrusion Detection System
IEC International Electrotechnical Commission
IED Intelligent Electronic Device
IEEE Institute of Electrical and Electronics Engineers
IETF Internet Engineering Task Force
IGMP Internet Group Management Protocol
INL Idaho National Laboratory
IP Internet Protocol
IPS Intrusion Prevention System
IPsec Internet Protocol Security
ISA The Instrumentation Systems and Automation Society
ISID Industrial Security Incident Database
ISO International Organization for Standardization
IT Information Technology
ITL Information Technology Laboratory
LAN Local Area Network
MAC Media Access Control
MES Manufacturing Execution System
MIB Management Information Base
MTU Master Terminal Unit (also Master Telemetry Unit)
NAT Network Address Translation
NCSD National Cyber Security Division
NERC North American Electric Reliability Council
NFS Network File System
NIC Network Interface Card
NISCC National Infrastructure Security Coordination Centre
NIST National Institute of Standards and Technology
NSTB National SCADA Testbed
OLE Object Linking and Embedding
OMB Office of Management and Budget
OPC OLE for Process Control
OS Operating System
OSI Open Systems Interconnection
PCSF Process Control System Forum
PDA Personal Digital Assistant
A-2

A-3
PIN Personal Identification Number
PID Proportional – Integral - Derivative
PIV Personal Identity Verification
PLC Programmable Logic Controller
PP Protection Profile
PPP Point-to-Point Protocol
R&D Research and Development
RADIUS Remote Authentication Dial In User Service
RBAC Role-Based Access Control
RFC Request for Comments
RMA Reliability, Maintainability, and Availability
RPC Remote Procedure Call
RPO Recovery Point Objective
RTO Recovery Time Objective
RTU Remote Terminal Unit (also Remote Telemetry Unit)
SC Security Category
SCADA Supervisory Control and Data Acquisition
SCP Secure Copy
SFTP Secure File Transfer Protocol
SIS Safety Instrumented System
SMTP Simple Mail Transfer Protocol
SNL Sandia National Laboratories
SNMP Simple Network Management Protocol
SP Special Publication
SPP-ICS System Protection Profile for Industrial Control Systems
SQL Structured Query Language
SSH Secure Shell
SSID Service Set Identifier
SSL Secure Sockets Layer
TCP Transmission Control Protocol
TCP/IP Transmission Control Protocol/Internet Protocol
TFTP Trivial File Transfer Protocol
TLS Transport Layer Security
UDP User Datagram Protocol
UPS Uninterruptible Power Supply
US-CERT United States Computer Emergency Readiness Team
USB Universal Serial Bus
VFD Variable Frequency Drive
VLAN Virtual Local Area Network
VPN Virtual Private Network
WAN Wide Area Network
XML Extensible Markup Language

Appendix B—Glossary of Terms
Selected terms used in the Guide to Industrial Control Systems (ICS) Security are defined below. Source
References for certain definitions are listed at the end of this appendix.
Alternating
Current Drive
Synonymous with Variable Frequency Drive (VFD). [28]
Access Control List
(ACL)
A mechanism that implements access control for a system resource by
enumerating the identities of the system entities that are permitted to access the
resources. [1]
Accreditation The official management decision given by a senior agency official to authorize
operation of an information system and to explicitly accept the risk to agency
operations (including mission, functions, image, or reputation), agency assets, or
individuals, based on the implementation of an agreed-upon set of security
controls. [11]
Actuator A pneumatic, hydraulic, or electrically powered device that supplies force and
motion so as to position a valve’s closure member at or between the open or closed
position. [22]
Alarm A device or function that signals the existence of an abnormal condition by
making an audible or visible discrete change, or both, so as to attract attention to
that condition. [20]
Antivirus Tools Software products and technology used to detect malicious code, prevent it from
infecting a system, and remove malicious code that has infected the system.
Application Server A computer responsible for hosting applications to user workstations. [28]
Attack An attempt to gain unauthorized access to system services, resources, or
information, or an attempt to compromise system integrity, availability, or
confidentiality.[2]
Authentication Verifying the identity of a user, process, or device, often as a prerequisite to
allowing access to resources in an information system. [11]
Authorization The right or a permission that is granted to a system entity to access a system
resource. [1]
Backdoor An undocumented way of gaining access to a computer system. A backdoor is a
potential security risk.
Batch Process A process that leads to the production of finite quantities of material by subjecting
quantities of input materials to an ordered set of processing activities over a finite
time using one or more pieces of equipment.[24]
Broadcast Transmission to all devices in a network without any acknowledgment by the
receivers. [18]
Buffer Overflow A condition at an interface under which more input can be placed into a buffer or
data holding area than the capacity allocated, overwriting other information.
Adversaries exploit such a condition to crash a system or to insert specially crafted
code that allows them to gain control of the system. [6]
B-1

Certification A comprehensive assessment of the management, operational, and technical
security controls in an information system, made in support of security
accreditation, to determine the extent to which the controls are implemented
correctly, operating as intended, and producing the desired outcome with respect
to meeting the security requirements for the system.[9]
Clear Text Information that is not encrypted.
Confidentiality Preserving authorized restrictions on information access and disclosure, including
means for protecting personal privacy and proprietary information. [11]
Configuration (of a
system or device)
Step in system design; for example, selecting functional units, assigning their
locations, and defining their interconnections. [17]
Configuration
Control
Process for controlling modifications to hardware, firmware, software, and
documentation to ensure the information system is protected against improper
modifications before, during, and after system implementation.[2]
Continuous Process A process that operates on the basis of continuous flow, as opposed to batch,
intermittent, or sequenced operations.
Control Algorithm A mathematical representation of the control action to be performed. [19]
Control Center An equipment structure or group of structures from which a process is measured,
controlled, and/or monitored. [21]
Control Loop A combination of field devices and control functions arranged so that a control
variable is compared to a set point and returns to the process in the form of a
manipulated variable.
Control Network Those networks of an enterprise typically connected to equipment that controls
physical processes and that is time or safety critical. The control network can be
subdivided into zones, and there can be multiple separate control networks within
one enterprise and site. [13]
Control Server A server that hosts the supervisory control system, typically a commercially
available application for DCS or SCADA system. [28]
Control System A system in which deliberate guidance or manipulation is used to achieve a
prescribed value for a variable. Control systems include SCADA, DCS, PLCs and
other types of industrial measurement and control systems.
Controlled Variable The variable that the control system attempts to keep at the set point value. The
set point may be constant or variable. [19]
Controller A device or program that operates automatically to regulate a controlled variable.
[21]
Cycle Time The time, usually expressed in seconds, for a controller to complete one control
loop where sensor signals are read into memory, control algorithms are executed,
and corresponding control signals are transmitted to actuators that create changes
the process resulting in new sensor signals. [19]
Database A repository of information that usually holds plantwide information including
process data, recipes, personnel data, and financial data. [28]
Data Historian A centralized database supporting data analysis using statistical process control
techniques.
DC Servo Drive A type of drive that works specifically with servo motors. It transmits commands
to the motor and receives feedback from the servo motor resolver or encoder. [28]
B-2

Denial of Service
(DoS)
The prevention of authorized access to a system resource or the delaying of system
operations and functions. [1]
Diagnostics Information concerning known failure modes and their characteristics. Such
information can be used in troubleshooting and failure analysis to help pinpoint the
cause of a failure and help define suitable corrective measures. [19]
Disaster Recovery
Plan (DRP)
A written plan for processing critical applications in the event of a major hardware
or software failure or destruction of facilities. [8]
Discrete Process A type of process where a specified quantity of material moves as a unit (part or
group of parts) between work stations and each unit maintains its unique identity.
[19]
Distributed Control
System (DCS)
In a control system, refers to control achieved by intelligence that is distributed
about the process to be controlled, rather than by a centrally located single unit. [19]
Distributed Plant A geographically distributed factory that is accessible through the Internet by an
enterprise. [28]
Disturbance An undesired change in a variable being applied to a system that tends to adversely
affect the value of a controlled variable.[21]
Domain Controller A server responsible for managing domain information, such as login
identification and passwords. [28]
Encryption Cryptographic transformation of data (called “plaintext”) into a form (called
“ciphertext”) that conceals the data’s original meaning to prevent it from being
known or used. If the transformation is reversible, the corresponding reversal
process is called “decryption”, which is a transformation that restores encrypted
data to its original state. [1]
Enterprise An organization that coordinates the operation of one or more processing sites. [24]
Enterprise
Resource Planning
(ERP) System
A system that integrates enterprise-wide information including human resources,
financials, manufacturing, and distribution as well as connects the organization to
its customers and suppliers.
Extensible Markup
Language (XML)
A specification for a generic syntax to mark data with simple, human-readable
tags, enabling the definition, transmission, validation, and interpretation of data
between applications and between organizations.
Fault Tolerant Of a system, having the built-in capability to provide continued, correct execution
of its assigned function in the presence of a hardware and/or software fault.
Field Device Equipment that is connected to the field side on an ICS. Types of field devices
include RTUs, PLCs, actuators, sensors, HMIs, and associated communications.
Field Site A subsystem that is identified by physical, geographical, or logical segmentation
within the ICS. A field site may contain RTUs, PLCs, actuators, sensors, HMIs,
and associated communications.
Fieldbus A digital, serial, multi-drop, two-way data bus or communication path or link
between low-level industrial field equipment such as sensors, transducers,
actuators, local controllers, and even control room devices. Use of fieldbus
technologies eliminates the need of point-to-point wiring between the controller
and each device. A protocol is used to define messages over the fieldbus network
with each message identifying a particular sensor on the network.
B-3

File Transfer
Protocol (FTP)
FTP is an Internet standard for transferring files over the Internet. FTP programs
and utilities are used to upload and download Web pages, graphics, and other files
between local media and a remote server which allows FTP access. [15]
Firewall An inter-network gateway that restricts data communication traffic to and from
one of the connected networks (the one said to be “inside” the firewall) and thus
protects that network’s system resources against threats from the other network
(the one that is said to be “outside” the firewall). [1]
Human-Machine
Interface (HMI)
The hardware or software through which an operator interacts with a controller.
An HMI can range from a physical control panel with buttons and indicator lights
to an industrial PC with a color graphics display running dedicated HMI software.
[28]
Identification The process of verifying the identity of a user, process, or device, usually as a
prerequisite for granting access to resources in an IT system. [10]
Incident An occurrence that actually or potentially jeopardizes the confidentiality, integrity,
or availability of an information system or the information the system processes,
stores, or transmits or that constitutes a violation or imminent threat of violation of
security policies, security procedures, or acceptable use policies. Incidents may be
intentional or unintentional. [4]
Input/Output (I/O) A general term for the equipment that is used to communicate with a computer as
well as the data involved in the communications. [19]
Insider An entity inside the security perimeter that is authorized to access system
resources but uses them in a way not approved by those who granted the
authorization. [1]
Integrity Guarding against improper information modification or destruction, and includes
ensuring information non-repudiation and authenticity. [11]
Intelligent
Electronic Device
(IED)
Any device incorporating one or more processors with the capability to receive or
send data/control from or to an external source (e.g., electronic multifunction
meters, digital relays, controllers). [14]
Internet The single interconnected world-wide system of commercial, government,
educational, and other computer networks that share the set of protocols specified
by the Internet Architecture Board (IAB) and the name and address spaces
managed by the Internet Corporation for Assigned Names and Numbers (ICANN).
[1]
Intrusion Detection
System (IDS)
A security service that monitors and analyzes network or system events for the
purpose of finding, and providing real-time or near real-time warning of, attempts
to access system resources in an unauthorized manner. [1]
Intrusion
Prevention System
(IPS)
A system that can detect an intrusive activity and can also attempt to stop the
activity, ideally before it reaches its targets.
Jitter The time or phase difference between the data signal and the ideal clock.
Key Logger A program designed to record which keys are pressed on a computer keyboard
used to obtain passwords or encryption keys and thus bypass other security
measures.
Light Tower A device containing a series of indicator lights and an embedded controller used to
indicate the state of a process based on an input signal. [28]
B-4

Local Area
Network (LAN)
A group of computers and other devices dispersed over a relatively limited area
and connected by a communications link that enables any device to interact with
any other on the network.
Machine Controller A control system/motion network that electronically synchronizes drives within a
machine system instead of relying on synchronization via mechanical linkage.
Maintenance Any act that either prevents the failure or malfunction of equipment or restores its
operating capability. [19]
Malware Software or firmware intended to perform an unauthorized process that will have
adverse impact on the confidentiality, integrity, or availability of an information
system. A virus, worm, Trojan horse, or other code-based entity that infects a host.
Spyware and some forms of adware are also examples of malicious code
(malware). [11]
Management
Controls
The security controls (i.e., safeguards or countermeasures) for an information
system that focus on the management of risk and the management of information
security.[5]
Manipulated
Variable
In a process that is intended to regulate some condition, a quantity or a condition
that the control alters to initiate a change in the value of the regulated condition.
[19]
Manufacturing
Execution System
(MES)
A system that uses network computing to automate production control and process
automation. By downloading recipes and work schedules and uploading
production results, a MES bridges the gap between business and plant-floor or
process-control systems. [28]
Master Terminal
Unit (MTU)
See SCADA Server.
Modem A device used to convert serial digital data from a transmitting terminal to a signal
suitable for transmission over a telephone channel to reconvert the transmitted
signal to serial digital data for the receiving terminal. [28]
Motion Control
Network
The network supporting the control applications that move parts in industrial
settings, including sequencing, speed control, point-to-point control, and
incremental motion. [19]
Network Interface
Card (NIC)
A circuit board or card that is installed in a computer so that it can be connected to
a network.
Object Linking and
Embedding (OLE)
for Process Control
(OPC)
A set of open standards developed to promote interoperability between disparate
field devices, automation/control, and business systems.
Operating System An integrated collection of service routines for supervising the sequencing of
programs by a computer. An operating system may perform the functions of
input/output control, resource scheduling, and data management. It provides
application programs with the fundamental commands for controlling the
computer. [19]
Operational
Controls
The security controls (i.e., safeguards or countermeasures) for an information
system that are primarily implemented and executed by people (as opposed to
systems). [5]
Password A string of characters (letters, numbers, and other symbols) used to authenticate an
identity or to verify access authorization.
B-5

Phishing Tricking individuals into disclosing sensitive personal information by claiming to
be a trustworthy entity in an electronic communication (e.g., internet web sites).
Photo Eye A light sensitive sensor utilizing photoelectric control that converts a light signal
into an electrical signal, ultimately producing a binary signal based on an
interruption of a light beam. [28]
Port The entry or exit point from a computer for connecting communications or
peripheral devices. [19]
Port Scanning Using a program to remotely determine which ports on a system are open (e.g.,
whether systems allow connections through those ports). [12]
Pressure Regulator A device used to control the pressure of a gas or liquid. [28]
Pressure Sensor A sensor system that produces an electrical signal related to the pressure acting on
it by its surrounding medium. [28]
Pressure sensors can also use differential
pressure to obtain level and flow measurements.
Printer A device that converts digital data to human-readable text on a paper medium.[28]
Process Controller A proprietary computer system, typically rack-mounted, that processes sensor
input, executes control algorithms, and computes actuator outputs. [28]
Programmable
Logic Controller
(PLC)
A solid-state control system that has a user-programmable memory for storing
instructions for the purpose of implementing specific functions such as I/O control,
logic, timing, counting, three mode (PID) control, communication, arithmetic, and
data and file processing. [19]
Protocol A set of rules (i.e., formats and procedures) to implement and control some type of
association (e.g., communication) between systems. [1]
Protocol Analyzer A device or software application that enables the user to analyze the performance
of network data so as to ensure that the network and its associated
hardware/software are operating within network specifications. [19]
Proximity Sensor A non-contact sensor with the ability to detect the presence of a target within a
specified range. [28]
Real-Time Pertaining to the performance of a computation during the actual time that the
related physical process transpires so that the results of the computation can be
used to guide the physical process. [28]
Redundant Control
Server
A backup to the control server that maintains the current state of the control server
at all times. [28]
Relay An electromechanical device that completes or interrupts an electrical circuit by
physically moving conductive contacts. The resultant motion can be coupled to
another mechanism such as a valve or breaker. [19]
Remote Access Access by users (or information systems) communicating external to an
information system security perimeter. [11]
Remote Diagnostics Diagnostics activities conducted by individuals communicating external to an
information system security perimeter.
Remote
Maintenance
Maintenance activities conducted by individuals communicating external to an
information system security perimeter.
Remote Terminal
Unit (RTU)
A computer with radio interfacing used in remote situations where
communications via wire is unavailable. Usually used to communicate with
remote field equipment. PLCs with radio communication capabilities are also
used in place of RTUs.
B-6

Resource
Starvation
A condition where a computer process cannot be supported by available computer
resources. Resource starvation can occur due to the lack of computer resources or
the existence of multiple processes that are competing for the same computer
resources.
Risk The level of impact on agency operations (including mission, functions, image, or
reputation), agency assets, or individuals resulting from the operation of an
information system, given the potential impact of a threat and the likelihood of that
threat occurring.[7]
Risk Assessment The process of identifying risks to agency operations (including mission,
functions, image, or reputation), agency assets, or individuals by determining the
probability of occurrence, the resulting impact, and additional security controls
that would mitigate this impact. Part of risk management, synonymous with risk
analysis. Incorporates threat and vulnerability analyses.[7]
Risk Management The process of managing risks to agency operations (including mission, functions,
image, or reputation), agency assets, or individuals resulting from the operation of
an information system. It includes risk assessment; cost-benefit analysis; the
selection, implementation, and assessment of security controls; and the formal
authorization to operate the system. The process considers effectiveness,
efficiency, and constraints due to laws, directives, policies, or regulations.[7]
Router A computer that is a gateway between two networks at OSI layer 3 and that relays
and directs data packets through that inter-network. The most common form of
router operates on IP packets. [1]
Router Flapping A router that transmits routing updates alternately advertising a destination
network first via one route, then via a different route.
Safety
Instrumented
System (SIS)
A system that is composed of sensors, logic solvers, and final control elements
whose purpose is to take the process to a safe state when predetermined conditions
are violated. Other terms commonly used include emergency shutdown system
(ESS), safety shutdown system (SSD), and safety interlock system (SIS). [23]
SCADA Server The device that acts as the master in a SCADA system. [28]
Security Audit Independent review and examination of a system’s records and activities to
determine the adequacy of system controls, ensure compliance with established
security policy and procedures, detect breaches in security services, and
recommend any changes that are indicated for countermeasures. [16]
Security Controls The management, operational, and technical controls (i.e., safeguards or
countermeasures) prescribed for an information system to protect the
confidentiality, integrity, and availability of the system and its information.[3]
Security Plan Formal document that provides an overview of the security requirements for the
information system and describes the security controls in place or planned for
meeting those requirements. [11]
Security Policy Security policies define the objectives and constraints for the security program.
Policies are created at several levels, ranging from organization or corporate policy
to specific operational constraints (e.g., remote access). In general, policies
provide answers to the questions “what” and “why” without dealing with “how.”
Policies are normally stated in terms that are technology-independent. [13]
Sensor A device that produces a voltage or current output that is representative of some
physical property being measured (e.g., speed, temperature, flow) [19]
B-7

Servo Valve An actuated valve whose position is controlled using a servo actuator. [28]
Set Point An input variable that sets the desired value of the controlled variable. This
variable may be manually set, automatically set, or programmed. [19]
Simple Network
Management
Protocol (SNMP)
A standard TCP/IP protocol for network management. Network administrators
use SNMP to monitor and map network availability, performance, and error rates.
To work with SNMP, network devices utilize a distributed data store called the
Management Information Base (MIB). All SNMP-compliant devices contain a
MIB which supplies the pertinent attributes of a device. Some attributes are fixed
or “hard-coded” in the MIB, while others are dynamic values calculated by agent
software running on the device. [15]
Single Loop
Controller
A controller that controls a very small process or a critical process. [28]
Social Engineering An attempt to trick someone into revealing information (e.g., a password) that can
be used to attack systems or networks. [12]
Solenoid Valve A valve actuated by an electric coil. A solenoid valve typically has two states:
open and closed. [28]
Spyware Software that is secretly or surreptitiously installed onto an information system to
gather information on individuals or organizations without their knowledge; a type
of malicious code. [11]
Statistical Process
Control (SPC)
The use of statistical techniques to control the quality of a product or process. [19]
Steady State A characteristic of a condition, such as value, rate, periodicity, or amplitude,
exhibiting only negligible change over an arbitrarily long period of time. [21]
Supervisory
Control
A term that is used to imply that the output of a controller or computer program is
used as input to other controllers. [19]
Supervisory
Control and Data
Acquisition
(SCADA)
A generic name for a computerized system that is capable of gathering and
processing data and applying operational controls over long distances. Typical
uses include power transmission and distribution and pipeline systems. SCADA
was designed for the unique communication challenges (e.g., delays, data
integrity) posed by the various media that must be used, such as phone lines,
microwave, and satellite. Usually shared rather than dedicated. [19]
Technical Controls The security controls (i.e., safeguards or countermeasures) for an information
system that are primarily implemented and executed by the information system
through mechanisms contained in the hardware, software, or firmware components
of the system.[5]
Temperature
Sensor
A sensor system that produces an electrical signal related to its temperature and, as
a consequence, senses the temperature of its surrounding medium. [28]
Threat Any circumstance or event with the potential to adversely impact agency
operations (including mission, functions, image, or reputation), agency assets, or
individuals through an information system via unauthorized access, destruction,
disclosure, modification of information, and/or denial of service. [11]
Transmission
Control Protocol
(TCP)
TCP is one of the main protocols in TCP/IP networks. Whereas the IP protocol
deals only with packets, TCP enables two hosts to establish a connection and
exchange streams of data. TCP guarantees delivery of data and also guarantees
that packets will be delivered in the same order in which they were sent. [15]
B-8

Trojan Horse A computer program that appears to have a useful function, but also has a hidden
and potentially malicious function that evades security mechanisms, sometimes by
exploiting legitimate authorizations of a system entity that invokes the program. [1]
Unauthorized
Access
A person gains logical or physical access without permission to a network, system,
application, data, or other resource. [12]
Valve An in-line device in a fluid-flow system that can interrupt flow, regulate the rate of
flow, or divert flow to another branch of the system. [19]
Variable Frequency
Drive (VFD)
A type of drive that controls the speed, but not the precise position, of a non-servo,
AC motor by varying the frequency of the electricity going to that motor. VFDs
are typically used for applications where speed and power are important, but
precise positioning is not. [28]
Virtual Private
Network (VPN)
A restricted-use, logical (i.e., artificial or simulated) computer network that is
constructed from the system resources of a relatively public, physical (i.e., real)
network (such as the Internet), often by using encryption (located at hosts or
gateways), and often by tunneling links of the virtual network across the real
network. [1]
Virus A hidden, self-replicating section of computer software, usually malicious logic,
that propagates by infecting (i.e., inserting a copy of itself into and becoming part
of) another program. A virus cannot run by itself; it requires that its host program
be run to make the virus active. [1]
Virus Definitions Predefined signatures for known malware used by antivirus detection algorithms.
Vulnerability Weakness in an information system, system security procedures, internal controls,
or implementation that could be exploited or triggered by a threat source. [11]
Wide Area
Network (WAN)
A physical or logical network that provides data communications to a larger
number of independent users than are usually served by a local area network
(LAN) and that is usually spread over a larger geographic area than that of a LAN.
[15]
Wireless Device A device that can connect to a manufacturing system via radio or infrared waves to
typically collect/monitor data, but also in cases to modify control set points. [28]
Workstation A computer used for tasks such as programming, engineering, and design. [28]
Worm A computer program that can run independently, can propagate a complete
working version of itself onto other hosts on a network, and may consume
computer resources destructively. [1]
B-9

B-10
Source References for Glossary Definitions
[1] RFC 4949, Internet Security Glossary, Version 2, August 2007, http://www.rfc-
editor.org/rfc/rfc4949.txt.
[2] National Information Assurance (IA) Glossary, CNSS Instruction no. 4009, revised June 2006.
[3] FIPS PUB 199, Standards for Security Categorization of Federal Information and Information
Systems, February 2004.
[4] FIPS PUB 200, Minimum Security Requirements for Federal Information and Information System,
March 2006.
[5] NIST SP 800-18 Revision 1, Guide for Developing Security Plans for Federal Information Systems,
February 2006.
[6] NIST SP 800-28, Guidelines on Active Content and Mobile Code, October 2001.
[7] NIST SP 800-30, Risk Management Guide for Information Technology Systems, July 2002.
[8] NIST SP 800-34, Contingency Planning Guide for Information Technology Systems, June 2002.
[9] NIST SP 800-37, Guide for Security Certification and Accreditation of Federal Information
Systems, May 2004.
[10] NIST SP 800-47, Security Guide for Interconnecting Information Technology Systems, Aug 2002.
[11] NIST SP 800-53 Revision 1, Recommended Security Controls for Federal Information Systems,
July 2006.
[12] NIST SP 800-61, Computer Security Incident Handling Guide, January 2004.
[13] ISA SP99 Glossary.
[14] AGA 12, Cryptographic Protection of SCADA Communications.
[15] API 1164, Pipeline SCADA Security, Second Edition.
[16] ISO/IEC 7498: Information processing systems – Open System Interconnection – Basic reference
Model, Part 2: Security Architecture.
[17] IEC/PAS 62409, Real-time Ethernet for Plant Automation, ed 1.0, (2005-06).
[18] IEC/PAS 62410, Real-time Ethernet SERCOS III, ed. 1.0 (2005-08).
[19] The Automation, Systems, and Instrumentation Dictionary, 4th
Edition, ISA, 2003.
[20] ANSI/ISA-5.1-2009, Instrumentation Symbols and Identification.
[21] ANSI/ISA-51.1-1979 - (R1993) - Process Instrumentation Terminology.
[22] ANSI/ISA-75.05.01-2000, Control Valve Terminology.
[23] ANSI/ISA-84.00.01, 2004.
[24] ANSI/ISA-88.01-1995 - Batch Control Part 1: Models and Terminology.
[25] Bailey, David, and Wright, Edwin, Practical SCADA for Industry, IDC Technologies, 2003.
[26] Boyer, Stuart, SCADA Supervisory Control and Data Acquisition, 2nd
Edition, ISA, 1999.
[27] Erickson, Kelvin, and Hedrick, John, Plant Wide Process Control, Wiley & Sons, 1999.
[28] Falco, Joe, et al., IT Security for Industrial Control Systems, NIST IR 6859, 2003,
http://www.isd.mel.nist.gov/documents/falco/ITSecurityProcess.pdf.

Appendix C—Current Activities in Industrial Control System Security
This appendix contains abstracts of some of the many activities that are currently addressing ICS cyber
security. Please be aware that organization descriptions and related information provided in this appendix
has been drawn primarily from the listed organizations’ Web sites and from other reliable public sources,
but has not been verified. Readers are encouraged to contact the organizations directly for the most up-to-
date and complete information.
American Gas Association (AGA) Standard 12, “Cryptographic Protection of SCADA
Communications”
Standard 12 Documents:
http://www.awwarf.org/research/TopicsAndProjects/Resources/SpecialReports/2969/
American Gas Association: http://www.aga.org/
The American Gas Association, representing 195 local energy utility organizations that deliver natural gas
to more than 56 million homes, businesses, and industries throughout the United States, advocates the
interests of its energy utility members and their customers, and provides information and services. The
AGA 12 series of documents recommends practices designed to protect SCADA communications against
cyber incidents. The recommended practices focus on ensuring the confidentiality of SCADA
communications. The document series, “Cryptographic Protection of SCADA Communications”, when
complete will consist of the following four documents:
AGA 12-1 Background, Policies and Test Plan
AGA 12-2 Retrofit Link Encryption for Asynchronous Serial Communications
AGA 12-3 Protection of Networked Systems
AGA 12-4 Protection Embedded in SCADA Components.
The purpose of the AGA 12 series is to save SCADA system owners’ time and effort by recommending a
comprehensive system designed specifically to protect SCADA communications using cryptography.
The AGA 12 series may be applied to water, wastewater, and electric SCADA-based distribution systems
because of their similarities with natural gas systems, however timing requirements may be different.
Recommendations included in the series 12 documents may also apply to other ICS. Additional topics
planned for future addendums in this series include key management, protection of data at rest, and
security policies.
American Petroleum Institute (API) Standard 1164, “Pipeline SCADA Security”
American Petroleum Institute: http://api-ec.api.org/
The American Petroleum Institute represents more than 400 members involved in all aspects of the oil
and natural gas industry. API 1164 provides guidance to the operators of oil and natural gas pipeline
systems for managing SCADA system integrity and security. The guideline is specifically designed to
provide operators with a description of industry practices in SCADA security, and to provide the
framework needed to develop sound security practices within the operator’s individual organizations. It
stresses the importance of operators understanding system vulnerability and risks when reviewing the
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SCADA system for possible system improvements. API 1164 provides a means to improve the security
of SCADA pipeline operations by:
Listing the processes used to identify and analyze the SCADA system’s susceptibility to incidents
Providing a comprehensive list of practices to harden the core architecture
Providing examples of industry recommended practices.
The guideline targets small to medium pipeline operators with limited IT security resources. The
guideline is applicable to most SCADA systems, not just oil and natural gas SCADA systems. The
appendices of the document include a checklist for assessing a SCADA system and an example of a
SCADA control system security plan.
Center for SCADA Security at Sandia National Laboratories (SNL)
http://www.sandia.gov/ccss
The Center for SCADA Security is composed of several test bed facilities, which allow real-world critical
infrastructure problems to be modeled, designed, simulated, verified, and validated. These labs are
integrated into a research effort focusing on solving current control system security problems and
developing next generation control systems. These facilities include the following:
Distributed Energy Technology Laboratory (DETL), which provides a platform to test the control
of operational generation and load systems
Network Laboratory, which provides network visualization and wired and wireless network
modeling
Cryptographic Research Facility, which supports research and development of encryption for
applications in control system networks
Red Team Facility, which provides a suite of tools to attack and analyze control system
vulnerabilities
Advanced Information Systems Lab, which is used to research intelligent technologies for
development of the infrastructures of the future.
Chemical Sector Cyber Security Program
http://www.chemicalcybersecurity.com/
The Chemical Sector Cyber Security Program is a strategic program of the Chemical Information
Technology Center (ChemITC) of the American Chemistry Council. The Chemical Sector Cyber
Security Program focuses on risk management and reduction to minimize the potential impact of cyber
attacks on business and manufacturing systems.
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Chemical Industry Data Exchange (CIDX)
http://www.cidx.org/
"At the end of 2008 CIDX transitioned its standards and operations to the Open Application Group, Inc.
(OAGi) and the American Chemistry Council’s Chemical Information Technology Center (ChemITC®),
and then ceased to exist as a corporation
Under the terms of the agreement, CIDX transfered its Chem eStandards® and other related intellectual
property to OAGi. OAGi will create a new Chemical Industry Council to provide ongoing support and
maintenance for these work products and contribute chemical industry requirements to the development
of the OAGIS standard. Chem eStandards will remain free and OAGi standards will be free.
DHS Control Systems Security Program (CSSP)
http://www.uscert.gov/control_systems/
The goal of the DHS National Cyber Security Division's CSSP is to reduce industrial control system risks
within and across all critical infrastructure and key resource sectors by coordinating efforts among
federal, state, local, and tribal governments, as well as industrial control systems owners, operators and
vendors. The CSSP coordinates activities to reduce the likelihood of success and severity of impact of a
cyber attack against critical infrastructure control systems through risk-mitigation activities.
The Industrial Control Systems Cyber Emergency Response Team (ICS-CERT) provides a control system
security focus in collaboration with US-CERT to:
Respond to and analyze control systems related incidents
Conduct vulnerability and malware analysis
Provide onsite support for incident response and forensic analysis
Provide situational awareness in the form of actionable intelligence
Coordinate the responsible disclosure of vulnerabilities/mitigations
Share and coordinate vulnerability information and threat analysis through information products and
alerts
The ICS-CERT serves as a key component of the Strategy for Securing Control Systems, which outlines a
long-term, common vision where effective risk management of control systems security can be realized
through successful coordination efforts.
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DHS CSSP Recommended Practices
http://www.us-cert.gov/control_systems/practices/
The DHS Control Systems Security Program (CSSP) Recommended Practices site provides a current
information resource to help industry understand and prepare for ongoing and emerging control systems
cyber security issues, vulnerabilities and mitigation strategies.
The CSSP works with the control systems community to ensure that recommended practices, which are
made available, have been vetted by subject-matter experts in industry before being made publicly
available in support of this program.
Recommended practices are developed to help users reduce their exposure and susceptibility to
cyber attacks. These recommendations are based on understanding the cyber threats, control
systems vulnerabilities and attack paths, and control systems engineering.
The practices recommended on this site are focused to increase security awareness and provide security
practices that have been recommended by industry to aid in a secure architecture. Additional
recommended practices and supporting documents that cover specific issues and associated mitigations
will continue to be added.
Electric Power Research Institute (EPRI)
http://www.epri.com/
The Electric Power Research Institute (EPRI) is a nonprofit center for public interest energy and
environmental research. EPRI brings together member organizations, the Institute's scientists and
engineers, and other leading experts to work collaboratively on solutions to the challenges of electric
power. These solutions span nearly every area of power generation, delivery, and use, including health,
safety, and environment. EPRI's members represent over 90% of the electricity generated in the United
States.
During 2006 and 2007, EPRI developed and executed the PowerSec Program to assess utility cyber
security and evaluate the gap between existing and recommended practices. Nine electric power
companies (EPUs) participated in this program. Six of those EPUs participated in a project to determine
their aggregate security posture. This report presents the results of that project.
The intent of the final report is to provide the EPUs that funded the PowerSec Program with a view of
their composite security posture. The project team developed a self-assessment framework to help
members to evaluate how their cyber security program compares with their peers and with the NERC
Critical Infrastructure Protection (CIP) standards. The team conducted six on-site cyber security
assessments and analyzed the results.
This report presents a 'snapshot' of security posture of six EPUs that participated in a security survey
during 2006 and 2007. The report presents the survey and its results.
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Institute of Electrical and Electronics Engineers, Inc. (IEEE)
http://www.ieee.org
IEEE 1686-2007 – Standard for Substation IED Cyber Security Capabilities. The functions and features
to be provided in substation intelligent electronic devices (lEDs) to accommodate critical infrastructure
protection programs are defined in this standard. Security regarding the access, operation, configuration,
firmware revision, and data retrieval from an IED is addressed in this standard. Communications for the
purpose of power system protection (teleprotection) is not addressed. Encryption for the secure
transmission of data both within and external to the substation, including supervisory control and data
acquisition, is not part of this standard as this is addressed in other efforts."
IEEE P1711 - Trial Use Standard for a Cryptographic Protocol for Cyber Security of Substation Serial
Links - This trial use standard defines a cryptographic protocol to provide integrity, and optional
confidentiality, for cyber security of serial links. It does not address specific applications or hardware
implementations, and is independent of the underlying communications protocol.
Institute for Information Infrastructure Protection (I3P)
http://www.thei3p.org/
The I3P is a consortium of leading national cyber security institutions, including academic research
centers, government laboratories, and non-profit organizations. It was founded in September 2001 to help
meet a well-documented need for improved research and development (R&D) to protect the nation's
information infrastructure against catastrophic failures. The institute's main role is to coordinate a
national cyber security R&D program and help build bridges between academia, industry, and
government. The I3P continues to work toward identifying and addressing critical research problems in
information infrastructure protection and opening information channels between researchers,
policymakers, and infrastructure operators. Currently, the I3P does the following:
Fosters collaboration among academia, industry, and government on pressing cyber security problems
Develops, manages, and supports national-scale research projects
Provides research fellowship opportunities to qualified post-doctoral researchers, faculty, and
research scientists
Hosts workshops, meetings, and events on cyber security and information infrastructure protection
issues
Builds and supports a knowledge base as an online vehicle for sharing and distributing information to
I3P members and others working on information security challenges.
Membership in the I3P Consortium is at the institutional level; individuals are not eligible. Membership
is open to not-for-profit research and academic institutions actively engaged in research and policy
focused on cyber security and information infrastructure protection.
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International Electrotechnical Commission (IEC) Technical Committees 65 and 57
http://www.iec.ch/
IEC is a standards organization that prepares and publishes international standards for all electrical,
electronic, and related technologies. These standards serve as a basis for creating national standards and
as references for drafting international tenders and contracts. IEC’s members include manufacturers,
providers, distributors, vendors, consumers, users, all levels of governmental agencies, professional
societies, trade associations, and standards developers from over 60 countries.
In 2004 the IEC Technical Sub-Committee 65C (Industrial Networks), through its working group WG13
(Cyber Security), started to address security issues - within the IEC 61784 standard – for field buses and
other industrial communication networks. Results of this work are outlined in part 4, entitled “Digital
data communications for measurement and control – Profiles for secure communications in industrial
networks”.
TC65 WG10 is working to extend this field level communication to address security standards across
common automation networking scenarios. The standard being drafted as a result of this work is IEC
62443, entitled “Security for industrial process measurement and control – Network and system security”.
It is based on a modular security architecture consisting of requirement sets. These modules are mapped
into ICS component and network architecture. The resulting requirements can then be formulated for use
as the basis for Requests for Proposals (RFP) for data communication standards, and security audits.
TC 57 is focused on Power Systems Management and Associated Information Exchange and is divided
up into a series of working groups. Each working group is comprised of members of national standards
committees from the countries that participate in the IEC. Each working group is responsible for the
development of standards within its domain. The current working groups are:
WG 3: Telecontrol protocols
WG 10: Power system IED communication and associated data models
WG 13: Energy management system application program interface
WG 14: System interfaces for distribution management
WG 15: Data and communication security
WG 16: Deregulated energy market communications
WG 17: Communications systems for distributed energy resources
WG 18: Hydroelectric power plants – communication for monitoring and control
WG 19: Interoperability within TC 57 in the long term
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ISA99 Industrial Automation and Control Systems Security Standards
http://www.isa.org/isa99
The ISA99 Committee is establishing standards, recommended practices, technical reports, and related
information that will define procedures for implementing electronically secure industrial automation and
control systems and security practices and assessing electronic security performance. Guidance is
directed toward those responsible for designing, implementing, or managing industrial automation and
control systems and shall also apply to users, system integrators, security practitioners, and control system
manufacturers and vendors.
The committee’s focus is to improve the confidentiality, integrity, and availability of components or
systems used for automation or control and provide criteria for procuring and implementing secure
control systems. Compliance with the committee’s guidance will improve industrial automation and
control system electronic security, and will help identify vulnerabilities and address them, thereby
reducing the risk of compromising confidential information or causing industrial automation control
system degradation or failure. There are several standards in the ISA99 series; some are complete and
some are in development. Each will cover a specific aspect or subset of the subject of industrial
automation and control systems security. The documents have been broken down into four main
categories:
ISA-99.01.xx: General Security Requirements for Industrial Automation and Control Systems:
The first set of documents in the ISA99 series contains requirements that span the rest of the
documents in the ISA99 series. The documents explain terminology, concepts, and models that apply
to the whole series and metrics that can be used to measure the performance of the security program
and countermeasures.
ISA-99.02.xx: Security Program Requirements for Industrial Automation and Control Systems:
The second set of documents in the ISA99 series concerns the establishment, operation, and
certification of security programs and is generally end-user focused. Much of the material in the ISA-
99.02.xx set of documents is based on management systems from information technology that has
been adapted to industrial automation and control systems.
ISA-99.03.xx: System-Level Technical Requirements for Industrial Automation and Control
Systems: The third set of documents in the ISA99 series specifies technical capabilities and
requirements for systems used in automation and control. These stem from the security program
requirements in the ISA-99.02.xx series, but are focused on the technical requirements needed to meet
the security program requirements. The scope of this series is very broad and contains everything
from end-user requirements for setting up their industrial networks to vendors combining multiple
features into a larger product.
ISA-99.04.xx: Component-Level Technical Requirements for Industrial Automation and
Control Systems: The fourth set of documents in the ISA99 series specifies technical capabilities
and requirements for individual components used in automation and control. These stem from the
system-level technical requirements in the ISA-99.03.xx series, but are focused on the individual
components that make up full systems. The components may be things such as embedded devices,
network hardware, computers, and software packages.
The ISA99 committee was formed in 1992 and at the time this document was published had produced two
technical reports and two standards documents, one of which superseded one of the technical reports. In
2009, IEC TC65/WG10 began working with ISA99 to publish the ISA99 document series internationally.
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This resulted in the currently published documents being republished as the IEC 62443 series. All future
documents and revisions to ISA99 documents are being reviewed and published both by ISA and IEC.
ISA100 Wireless Systems for Automation
http://www.isa.org/isa100
The ISA100 Committee will establish standards, recommended practices, technical reports, and related
information that will define procedures for implementing wireless systems in the automation and control
environment with a focus on the field level. Guidance is directed towards those responsible for the
complete life cycle including the designing, implementing, on-going maintenance, scalability or
managing industrial automation and control systems, and shall apply to users, system integrators,
practitioners, and control systems manufacturers and vendors.
ISO/IEC 27002:2005 Security Techniques - Code of Practice for Information Security
Management
http://www.iso.org/, http://www.27000.org
ISO/IEC 27002:2005 comprises ISO/IEC 17799:2005 and ISO/IEC 17799:2005/Cor.1:2007. Its technical
content is identical to that of ISO/IEC 17799:2005. ISO/IEC 17799:2005/Cor.1:2007 changes the
reference number of the standard from 17799 to 27002.
ISO/IEC 27002:2005 establishes guidelines and general principles for initiating, implementing,
maintaining, and improving information security management in an organization. The objectives outlined
provide general guidance on the commonly accepted goals of information security management. ISO/IEC
27002:2005 contains best practices of control objectives and controls in the following areas of
information security management:
Security policy
Organization of information security
Asset management
Human resource security
Physical and environmental security
Communications and operations management
Access control
Information systems acquisition, development and maintenance
Information security incident management
Business continuity management
Compliance.
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The control objectives and controls in ISO/IEC 27002:2005 are intended to be implemented to meet the
requirements identified by a risk assessment. ISO/IEC 27002:2005 is intended as a common basis and
practical guideline for developing organizational security standards and effective security management
practices, and to help build confidence in inter-organizational activities.
ISO/IEC 27001:2005 Information technology – Security techniques – Information security
management systems – Requirements
ISO/IEC 27001:2005 provides a model for establishing, implementing, operating, monitoring, reviewing,
maintaining and improving an Information Security Management System. This standard adopts the
“Plan-Do-Check-Act” model. This standard covers all types of organizations and specifies the
requirements for an Information Security Management System within the context of the organization’s
overall business risks. The normative control objectives and controls addressed by this standard include:
Security policy
Organization of information security
Asset management
Human resource security
Physical and environmental security
Communications and operations management
Access control
Information systems acquisition, development and maintenance
Information security incident management
Business continuity management
Compliance.
International Council on Large Electric Systems (CIGRE)
http://www.cigre.org/
The International Council on Large Electric Systems (CIGRE) is a nonprofit international association
based in France. It has established several study committees to promote and facilitate the international
exchange of knowledge in the electrical industry by identifying recommended practices and developing
recommendations. Three of its study committees focus on control systems:
The objectives of the B3 Substations Committee include the adoption of technological advances in
equipment and systems to achieve increased reliability and availability.
The C2 System Operation and Control Committee focuses on the technical capabilities needed for the
secure and economical operation of existing power systems including control centers and operators.
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The D2 Information Systems and Telecommunication for Power Systems Committee monitors
emerging technologies in the industry and evaluates their possible impact. In addition, it focuses on
the security requirements of the information systems and services of control systems.
LOGIIC – Linking the Oil and Gas Industry to Improve Cyber Security
http://www.cyber.st.dhs.gov/logiic.html
LOGIIC is a unique collaborative forum where government and industry are focusing on cyber security
issues for the oil and gas industry that are best addressed collaboratively. The needs of the infrastructure
owners and operators are driving the formation of projects, supported by government and independent
experts. The forms for future collaboration are currently being established, and new projects will be
forthcoming.
National SCADA Test Bed (NSTB)
http://www.inl.gov/scada/
The DOE Office of Electricity Delivery and Energy Reliability (OE) seeks to improve the security and
reliability of our Nation’s energy delivery systems. OE established the National SCADA Test Bed
(NSTB) to help the energy sector and equipment vendors assess control system vulnerabilities and test the
security of control systems hardware and software. Working in partnership with the energy sector, the
National SCADA Test Bed seeks to:
Identify and mitigate existing vulnerabilities.
Facilitate development of security standards.
Serve as an independent entity to test SCADA systems and related control system technologies.
Identify and promote best cyber security practices.
Increase awareness of control systems security within the energy sector.
Develop advanced control system architectures and technologies that are more secure and robust.
Partners in the NSTB include Idaho National Laboratory, Sandia National Laboratories, Argonne
National Laboratory, Pacific Northwest National Laboratory, and the National Institute of Standards and
Technology.
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NIST 800 Series Security Guidelines
http://csrc.nist.gov/publications/nistpubs/index.html
The NIST Special Publication 800 series of documents on information technology reports on the NIST
Information Technology Laboratory (ITL) research, guidance, and outreach efforts in computer security,
and its collaborative activities with industry, government, and academic organizations. Focus areas
include cryptographic technology and applications, advanced authentication, public key infrastructure,
internetworking security, criteria and assurance, and security management and support. In addition to
NIST SP 800-82, the following is a listing of some additional 800 series documents that have significant
relevance to the ICS security community. These as well as many others are available through the URL
listed above.
NIST SP 800-18 Revision 1, Guide for Developing Security Plans for Federal Information Systems
NIST SP 800-37, Guide for Applying the Risk Management Framework to Federal Information
Systems: A Security Life Cycle Approach
NIST SP 800-39, Managing Information Security Risk: Organization, Mission, and Information
System View
NIST SP 800-40 Version 2, Creating a Patch and Vulnerability Management Program
NIST SP 800-41, Revision 1, Guidelines on Firewalls and Firewall Policy
NIST SP 800-48, Wireless Network Security: 802.11, Bluetooth, and Handheld Devices
NIST SP 800-50, Building an Information Technology Security Awareness and Training Program
NIST SP 800-53 Revision 3, Recommended Security Controls for Federal Information Systems and
Organizations
NIST SP 800-53A, Guide for Assessing the Security Controls in Federal Information Systems and
Organizations, Building Effective Security Assessment Plans
NIST SP 800-61, Computer Security Incident Handling Guide
NIST SP 800-63, Electronic Authentication Guideline
NIST SP 800-64, Security Considerations in the Information System Development Life Cycle
NIST SP 800-70, Security Configuration Checklists Program for IT Products—Guidance for
Checklists Users and Developers
NIST SP 800-77, Guide to IPSec VPNs
NIST SP 800-83, Guide to Malware Incident Prevention and Handling
NIST SP 800-86, Guide to Integrating Forensic Techniques into Incident Response
NIST SP 800-88, Guidelines for Media Sanitization
NIST SP 800-92, Guide to Computer Security Log Management
NIST SP 800-94, Guide to Intrusion Detection and Prevention Systems (IDPS)
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NIST SP 800-97, Guide to IEEE 802.11i: Robust Security Networks
NIST SP 800-100, Information Security Handbook: A Guide for Managers
NIST SP 800-111, Guide to Storage Encryption Technologies for End User Devices
NIST SP 800-115, Technical Guide to Information Security Testing and Assessment
NIST SP 800-123, Guide to General Server Security
NIST SP 800-127, Guide to Securing WiMAX Wireless Communications
NIST SP 800-128, Guide for Security Configuration Management of Information Systems
NIST Industrial Control System Security Project
http://csrc.nist.gov/groups/SMA/fisma/ics/
Because today’s ICS are often a combination of legacy systems, often with a planned life span of twenty
to thirty years, or a hybrid of legacy systems augmented with newer hardware and software that are
interconnected to other systems, it is often difficult or infeasible to apply some of the security controls
contained in NIST SP 800-53. Recognizing this problem, NIST has initiated the Industrial Control
System Security project in cooperation with the public and private sector ICS community to develop
specific guidance on the application of NIST documents, including the security controls in NIST SP 800-
53 to ICS. To facilitate the understanding of applying NIST SP 800-53 to ICS, a series of ICS cyber
security case studies were developed using actual ICS cyber security incidents. These case histories
examine the NIST SP 800-53 ICS controls that were violated or not implemented, and postulate the
potential mitigations that may have occurred if the controls had been implemented.
North American Electric Reliability Corporation (NERC)
http://www.nerc.com/
NERC’s mission is to improve the reliability and security of the bulk power system in North America. To
achieve that, NERC develops and enforces reliability standards; monitors the bulk power system; assesses
future adequacy; audits owners, operators, and users for preparedness; and educates and trains industry
personnel. NERC is a self-regulatory organization that relies on the diverse and collective expertise of
industry participants. As the Electric Reliability Organization, NERC is subject to audit by the U.S.
Federal Energy Regulatory Commission and governmental authorities in Canada
NERC has issued a set of cyber security standards to reduce the risk of compromise to electrical
generation resources and high-voltage transmission systems above 100kV, also referred to as bulk electric
systems. Bulk electric systems include Balancing Authorities, Reliability Coordinators, Interchange
Authorities, Transmission Providers, Transmission Owners, Transmission Operators, Generation Owners,
Generation Operators, and Load Serving Entities. The cyber security standards include audit measures
and levels of non-compliance that can be tied to penalties.
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C-13
The set of NERC Cyber Security Standards includes the following:
CIP-002 Critical Cyber Asset Identification
CIP-003 Security Management Controls
CIP-004 Personnel and Training
CIP-005 Electronic Security Perimeter(s)
CIP-006 Physical Security of Critical Cyber Assets
CIP-007 Systems Security Management
CIP-008 Incident Reporting and Response Planning
CIP-009 Recovery Plans for Critical Cyber Assets
The standards can be downloaded at: http://www.nerc.com/page.php?cid=2|20
SCADA and Control Systems Procurement Project
http://www.msisac.org/scada/
The SCADA Procurement Project, established in March 2006, is a joint effort among public and private
sectors focused on development of common procurement language that can be used by everyone. The
goal is for federal, state and local asset owners and regulators to come together using these procurement
requirements and to maximize the collective buying power to help ensure that security is integrated into
SCADA systems.
Smart Grid Interoperability Panel (SGIP) Cyber Security Working Group (CSWG)
http://collaborate.nist.gov/twiki-sggrid/bin/view/SmartGrid/CyberSecurityCTG
The primary goal of the working group is to develop an overall cyber security strategy for the Smart Grid
that includes a risk mitigation strategy to ensure interoperability of solutions across different
domains/components of the infrastructure. The cyber security strategy needs to address prevention,
detection, response, and recovery. Implementation of a cyber security strategy requires the definition and
implementation of an overall cyber security risk assessment process for the Smart Grid.
The working group’s effort is documented in NIST IR 7628 Guidelines for Smart Grid Cyber Security
http://csrc.nist.gov/publications/PubsNISTIRs.html#NIST-IR-7628

Appendix D—Emerging Security Capabilities
This section provides an overview of security capabilities that are available to or being developed in
support of the ICS community. There are several security products that are marketed specifically for ICS,
while others are general IT security products that are being used with ICS. Many of the products
available offer “single point solutions”, where a single security product offers multiple levels of
protection. In addition to available products, this section also discusses some research and development
work towards new products and technologies.
Encryption
Encryption protects the confidentiality of data by encoding the data to ensure that only the intended
recipient can decode it. There are some commercially available encryption products designed
specifically for ICS applications, as well as general encryption products that support basic serial and
Ethernet-based communications.
In addition to these products, the ICS SCADA community is working to develop a standard for
implementing the encryption of SCADA communications. The American Gas Association is working to
develop a standard, AGA-12, Cryptographic Protection of SCADA Communications, to protect SCADA
master-slave communication links from a variety of active and passive cyber attacks by developing a set
of standards to secure serial communication links using encryption. The AGA effort is broken into four
parts, with each addressing different aspects of SCADA communication protection:
AGA 12-1 summarizes cyber security policies, the background of the cyber security problem, and a
procedure for testing cryptographic protection systems.
AGA 12-2 is a detailed technical specification for building interoperable cryptographic modules to
protect SCADA communications for low-speed legacy SCADA systems and dial-up maintenance
ports.
AGA 12-3 will describe how to protect high-speed SCADA communications over networked
systems.
AGA 12-4 will describe how to build next-generation SCADA systems with embedded AGA 12
compatible cryptography.
Because of the long life of SCADA systems, a decision was made by AGA to focus initial efforts on the
protection of legacy systems. This decision has led to the near completion of parts 1 and 2, while parts 3
and 4 are still in the planning stages.
D-1

Firewalls
Firewalls are commonly used to segregate networks to protect and isolate ICS. These implementations
use commercially available firewalls that are focused on Internet and corporate application layer protocols
and are not equipped to handle ICS protocols. The ICS community is investigating the possibility of
adding protocol awareness to filtering devices. Research was performed by an IT security vendor in 2003
to develop a Modbus-based firewall that allows policy decisions to be made on Modbus/TCP header
values just as traditional firewalls filter on TCP/UDP ports and IP addresses [75]. There are currently
efforts to develop industrial firewalls.
Intrusion Detection and Prevention
Intrusion detection systems (IDS) and intrusion prevention systems (IPS) are being deployed on ICS
networks and components to detect well-known cyber attacks. Network IDS products monitor network
traffic and use various detection methods, such as comparing portions of the traffic to signatures of
known attacks. In contrast, host intrusion detection uses software loaded on a host computer, often with
attack signatures, to monitor ongoing events and data on a computer system for possible exploits. IPS
products take intrusion detection a step further by automatically acting on detected exploits to attempt to
stop them [56].
The required task of a security team to constantly monitor, evaluate, and quickly respond to intrusion
detection events is sometimes contracted to a managed security service provider (MSSP). MSSPs have
correlation and analysis engines to process and reduce the vast amounts of events logged per day to a
small subset that needs to be manually evaluated. There are also correlation and analysis engine products
available to large organizations wanting to perform this function in-house. Security information and
event management (SIEM) products are used in some organizations to monitor, analyze, and correlate
events from IDS and IPS logs, as well as audit logs from other computer systems, applications,
infrastructure equipment, and other hardware and software, to look for intrusion attempts.
Current IDS and IPS products are effective in detecting and preventing many well-known Internet attacks,
but until recently they have not addressed ICS protocol attacks. IDS and IPS vendors are beginning to
develop and incorporate attack signatures for various ICS protocols such as Modbus, DNP, and ICCP.
One cooperative effort within the ICS community is developing Snort rules for Modbus TCP, DNP3, and
ICCP. Snort is an open source network intrusion detection and prevention system using a rule-driven
language to perform signature, protocol, and anomaly-based inspections. The current rule sets, covering
Modbus, DNP, and ICCP, are basic, and efforts are underway to expand them. This same industry group
is also defining a data dictionary of log entries from various ICS applications. The data dictionary helps
cyber security monitoring products and services identify and understand the meaning of security events in
ICS application logs using normalized events. The dictionary is still under development. Some
commercial IDS and IPS vendors are also offering some ICS protocol signatures. [57].
As with any software added to an ICS component, the addition of host IDS or IPS software could affect
system performance. IPSs are commonplace in today’s information security industry, but can be very
resource intensive. These systems have the ability to automatically reconfigure systems if an intrusion
attempt is identified. This automated and fast reaction is designed to prevent successful exploits;
however, an automated tool such as this could be used by an adversary to adversely effect the operation
on an ICS by shutting down segments of a network or server. False positives can also hinder ICS
operation.
D-2

D-3
Malware/Antivirus Software
Because early malware threats were primarily viruses, the software to detect and remove malware has
historically been called “antivirus software”, even though it can detect many types of malware. Antivirus
software is used to counter the threats of malware by evaluating files on a computer’s storage devices
(some tools also detect malware in real-time at the network perimeter and/or on the user’s workstation)
against an inventory of malware signature files. If one of the files on a computer matches the profile of
known malware, the malware is removed through a disinfection process so it cannot infect other local
files or communicate across a network to infect other files on other computers. There are also techniques
available to identify unknown malware “in-the-wild” when a signature file is not yet available.
Many end-users and vendors of ICS are recommending the use of COTS antivirus software with their
systems and have even developed installation and configuration guidance based on their own laboratory
testing. Some ICS vendors recommend the use of antivirus software with their products, but offer little to
no guidance. Some end users and vendors are hesitant to use antivirus software due to fears that its use
would cause ICS performance problems or even failure. NIST and Sandia National Laboratories (SNL)
are conducting a study and producing a report aimed at helping ICS owners/operators to deploy antivirus
software and to minimize and assess performance impacts of workstation and server-based antivirus
products. This study has assembled ICS-based antivirus knowledge and serves as a starting point or a
secondary resource when installing, configuring, running, and maintaining antivirus software on an ICS
[55]. In many cases, performance impacts can be reduced through configuration settings as well as
antivirus scanning and maintenance scheduling outside of the antivirus software practices recommended
for typical IT systems.
In summary, COTS antivirus software can be used successfully on most ICS components. However,
special ICS specific considerations should be taken into account during the selection, installation,
configuration, operational, and maintenance procedures. ICS end-users should consult with the ICS
vendors regarding the use of antivirus software and can also use the output of the NIST and SNL study as
supplemental information.
Vulnerability and Penetration Testing Tools
There are many tools available for performing network vulnerability assessments and penetration tests for
typical IT networks; however, the impacts these tools may have on the operation of an ICS should be
carefully considered [76]. The additional traffic and exploits used during active vulnerability and
penetration testing, combined with the limited resources of many ICS, have been known to cause ICS to
malfunction. As guidance in this area, SNL has developed a preferred list of vulnerability and penetration
testing techniques for ICS [76]. These are less intrusive methods, passive instead of active, to collect the
majority of information that is often queried by automated vulnerability and penetration testing tools.
These methods are intended to allow collection of the necessary vulnerability information without the risk
of causing a failure while testing.
ICS owners must make the individuals using vulnerability and penetration testing tools aware of the
criticality of continuous operation and the risks involved with performing these tests on operational
systems. It may be possible to mitigate these risks by performing tests on ICS components such as
redundant servers or independent test systems in a laboratory setting. Laboratory tests can be used to
screen out test procedures that might harm the operational system. Even with very good configuration
management to assure that the test system is highly representative, tests on the actual system are likely to
uncover flaws not represented in the laboratory.

Appendix E—Industrial Control Systems in the FISMA Paradigm
In recognition of the importance of information security to the economic and national interests of the
United States, the Federal Information Security Management Act (FISMA) [13] was established to
require each Federal agency to develop, document, and implement an agency-wide program to provide
information security for the information and information systems that support the operations and assets of
the agency. The NIST FISMA Implementation Project [14] was established in January 2003 to produce
several key security standards and guidelines required by Congressional legislation including:
Standards to categorize information and information systems based on the objectives of providing
appropriate levels of information security according to a range of risk levels
Guidelines recommending the types of information and information systems to be included in each
category
Minimum information security requirements (i.e., management, operational, and technical controls)
for information and information systems in each category.
Key FISMA-related publications include Federal Information Processing Standards (FIPS) 199, FIPS
200, and NIST SPs 800-18, 800-37, 800-39, 800-53, 800-53A, 800-59 and 800-60. NIST has initiated the
Industrial Control System Security project22
in cooperation with the public and private sector ICS
community to develop specific guidance on the application of FISMA documents, including the security
controls in NIST SP 800-53, to ICS. Below is a listing of NIST FIPS and SPs documenting these
standards and guidelines.23
FIPS Publication 199: Standards for Security Categorization of Federal Information and
Information Systems contains standards to categorize information and information systems based on
the objectives of providing appropriate levels of information security according to a range of risk
levels [15]. The security categories are based on the potential impact on an organization should
certain events occur which jeopardize the information and information systems needed by the
organization to accomplish its assigned mission, protect its assets, fulfill its legal responsibilities,
maintain its day-to-day functions, and protect individuals. Security categories are to be used in
conjunction with vulnerability and threat information in assessing the risk to an organization resulting
from the operation of its information systems.
FIPS Publication 200: Minimum Security Requirements for Federal Information and
Information Systems specifies minimum security requirements for information and information
systems supporting the executive agencies of the Federal government and a risk-based process for
selecting the security controls necessary to satisfy the minimum security requirements [16]. The
document provides links to NIST SP 800-53 (Recommended Security Controls for Federal
Information Systems and Organizations), which recommends management, operational, and technical
controls needed to protect the confidentiality, integrity, and availability of all Federal information
systems that are not national security systems.
NIST SP 800-18: Guide for Developing Security Plans for Information Systems contains
guidelines to develop, document, and implement an agency-wide information security program that
includes subordinate plans for providing adequate information security for networks, facilities, and
systems or groups of information systems [17].
22
23
All of these publications are available from the NIST Computer Security Resource Center (CSRC) Web site, located at
http://csrc.nist.gov/.
E-1

NIST SP 800-30: Risk Management Guide for Information Technology Systems has guidelines
to develop an agency-wide information security program that includes periodic assessment of the risk
and magnitude of the harm that could result from unauthorized access, use disclosure, disruption,
modifications, or destruction of information and information systems.
NIST SP 800-37: Guide for the Security Certification and Accreditation of Federal Information
Systems provides guidance for applying the Risk Management Framework to federal information
systems to include conducting the activities of security categorization, security control selection and
implementation, security control assessment, information system authorization, and security control
monitoring [20].
NIST SP 800-39: Managing Information Security Risk provides guidance for an integrated,
organization-wide program for managing information security risk to organizational operations (i.e.,
mission, functions, image, and reputation), organizational assets, individuals, other organizations, and
the Nation resulting from the operation and use of federal information systems. Special Publication
800-39 provides a structured, yet flexible approach for managing risk that is intentionally broad-
based, with the specific details of assessing, responding to, and monitoring risk on an ongoing basis
provided by other supporting NIST security standards and guidelines [19].
NIST SP 800-53: Recommended Security Controls for Federal Information Systems and
Organizations provides guidelines for selecting and specifying security controls for information
systems supporting the executive agencies of the Federal government [21]. The guidelines apply to
all components of an information system that process, store, or transmit Federal information with the
exception of systems designated as national security systems.
NIST SP 800-53A: Guide for Assessing Security Controls in Federal Information Systems and
Organizations, Building Effective Security Assessment Plans provides guidance for conducting
periodic testing and evaluation of the effectiveness of information security policies, procedures, and
practices (including management, operational, and technical security controls) [22].
NIST SP 800-59: Guideline for Identifying an Information System as a National Security
System provides guidelines developed in conjunction with the Department of Defense, including the
National Security Agency, for identifying an information system as a national security system [23].
NIST SP 800-60: Guide for Mapping Types of Information and Information Systems to
Security Categories presents guidelines that recommend the types of information and information
systems to be included in each security category defined in FIPS 199 [24].
NIST SP 800-70: Security Configuration Checklists Program for IT Products: Guidance for
Checklists Users and Developers discusses the development of security configuration checklists and
option selections that minimize the security risks associated with commercial IT products used within
the Federal government [25].24
24
More information on this program is available at http://checklists.nist.gov/.
E-2

This set of documents provides security standards and guidelines that support an enterprise-wide risk
management process. The documents are intended to be an integral part of a Federal agency’s overall
information security program. The Risk Management Framework, illustrated in Figure E-1, provides a
disciplined and structured process that integrates information security and risk management activities into
the system development life. NIST SP 800-37 provides guidance applying the Risk Management
Framework to federal information systems to include conducting the activities of security
categorization,25
security control selection and implementation, security control assessment, information
system authorization,26
and security control monitoring.
Figure E-1. Risk Management Framework
The following is a chronological listing of the Risk Management Framework activities, a description of
each activity, and identification of supporting NIST documents. [26]
Categorize Information System
The first activity in the Risk Management Framework is to categorize the information and information
system according to potential impact of loss. For each information type and information system under
25
FIPS 199 provides security categorization guidance for nonnational security systems. CNSS Instruction 1253 provides similar
guidance for national security systems.
26
Security authorization is the official management decision given by a senior organizational official to authorize operation of an
information system and to explicitly accept the risk to organizational operations and assets, individuals, other organizations,
and the Nation based on the implementation of an agreed-upon set of security controls.
Starting
Point
RISK
MANAGEMENT
FRAMEWORK
PROCESS
OVERVIEW
Architecture Description
Architecture Reference Models
Segment and Solution Architectures
Mission and Business Processes
Information System Boundaries
Organizational Inputs
Laws, Directives, Policy Guidance
Strategic Goals and Objectives
Priorities and Resource Availabi tyli
Supply Chain Considerations
Repeat as necessary
Step 6
MONITOR
Security Controls
Step 2
SELECT
Security Controls
Step 3
IMPLEMENT
Security Controls
Step 4
ASSESS
Security Controls
Step 5
AUTHORIZE
Information System
Step 1
CATEGORIZE
Information System
E-3

consideration, the three FISMA-defined security objectives—confidentiality, integrity, and availability—
are associated with one of three levels of potential impact should there be a breach of security. It is
important to remember that for an ICS, availability is generally the greatest concern.
The generalized format for expressing the Security Category (SC) is:
SC information type or system = {(confidentiality, impact), (integrity, impact), (availability, impact)},
where the acceptable values for potential impact are LOW, MODERATE, or HIGH.
The standards and guidance for this categorization process can be found in FIPS 199 and NIST SP 800-
60, respectively. NIST is in the process of updating NIST SP 800-60 to provide additional guidance on
the categorization of ICS.
FIPS 199 establishes security categories for both information and information systems. The security
categories are based on the potential impact on an organization should certain events occur which
jeopardize the information and information systems needed by the organization to accomplish its assigned
mission, protect its assets, fulfill its legal responsibilities, maintain its day-to-day functions, and protect
individuals. Security categories are to be used in conjunction with vulnerability and threat information in
assessing the risk to an organization.
The security category of an information type can be associated with both user information and system
information and can be applicable to information in either electronic or non-electronic form. It can also
be used as input in considering the appropriate security category of an information system. Establishing
an appropriate security category of an information type essentially requires determining the potential
impact for each security objective associated with the particular information type.
Determining the security category of an information system requires slightly more analysis and must
consider the security categories of all information types resident on the information system. For an
information system, the potential impact values assigned to the respective security objectives
(confidentiality, integrity, availability) are the highest values (i.e., high water mark) from among those
security categories that have been determined for each type of information resident on the information
system.
The following example is taken from FIPS 199:
A power plant contains a SCADA system controlling the distribution of electric power for a large military
installation. The SCADA system contains both real-time sensor data and routine administrative
information. The management at the power plant determines that: (i) for the sensor data being acquired
by the SCADA system, there is no potential impact from a loss of confidentiality, a high potential impact
from a loss of integrity, and a high potential impact from a loss of availability; and (ii) for the
administrative information being processed by the system, there is a low potential impact from a loss of
confidentiality, a low potential impact from a loss of integrity, and a low potential impact from a loss of
availability. The resulting security categories, SC, of these information types are expressed as:
SC sensor data = {(confidentiality, NA), (integrity, HIGH), (availability, HIGH)},
and
SC administrative information = {(confidentiality, LOW), (integrity, LOW), (availability, LOW)}.
The resulting security category of the information system is initially expressed as:
E-4

SC SCADA system = {(confidentiality, LOW), (integrity, HIGH), (availability, HIGH)},
representing the high water mark or maximum potential impact values for each security objective from
the information types resident on the SCADA system. The management at the power plant chooses to
increase the potential impact from a loss of confidentiality from low to moderate, reflecting a more
realistic view of the potential impact on the information system should there be a security breach due to
the unauthorized disclosure of system-level information or processing functions. The final security
category of the information system is expressed as:
SC SCADA system = {(confidentiality, MODERATE), (integrity, HIGH), (availability, HIGH)}.
FIPS 199 specifies that information systems be categorized as low-impact, moderate-impact, or high-
impact for the security objectives of confidentiality, integrity, and availability. Possible definitions for
low, moderate, and high levels of security based on impact for ICS based on ISA99 are provided in Table
E-1. Possible definitions for ICS impact levels based on product produced, industry and security
concerns are provided in Table E-2.
Table E-1. Possible Definitions for ICS Impact Levels Based on ISA99
Impact Category Low-Impact Moderate-Impact High-Impact
Injury Cuts, bruises requiring
first aid
Requires hospitalization Loss of life or limb
Financial Loss $1,000 $100,000 Millions
Environmental Release Temporary damage Lasting damage Permanent damage, off-
site damage
Interruption of
Production
Minutes Days Weeks
Public Image Temporary damage Lasting damage Permanent damage
Table E-2. Possible Definitions for ICS Impact Levels Based on Product Produced, Industry and Security
Concerns
Category Low-Impact Moderate-Impact High-Impact
Product Produced • Non-hazardous
materials or products
• Non-ingested
consumer products
• Some hazardous
products or steps during
production
• High amount of
proprietary information
• Critical infrastructure
(e.g., electricity)
• Hazardous materials
• Ingested products
Industry Examples • Plastic injection
molding
• Warehouse
applications
• Automotive metal
industries
• Pulp and paper
• Semiconductors
• Utilities
• Petrochemical
• Food and beverage
• Pharmaceutical
Security Concerns • Protection against
minor injuries
• Ensuring uptime
• Protection against
moderate injuries
• Ensuring uptime
• Capital investment
• Protection against major
injuries/loss of life
• Ensuring uptime
• Capital investment
• Trade secrets
• Ensuring basic social
services
• Regulatory compliance
E-5

Select Security Controls
This framework activity includes the initial selection of minimum security controls planned or in place to
protect the information system based on a set of requirements. FIPS PUB 200 documents a set of
minimum-security requirements covering 17 security-related areas with regard to protecting the
confidentiality, integrity, and availability of Federal information systems and the information processed,
stored, and transmitted by those systems. The security-related areas are:
Access Control (AC)
Awareness and Training (AT)
Audit and Accountability (AU)
Security Assessment and Authorization (CA)
Configuration Management (CM)
Contingency Planning (CP)
Identification and Authentication (IA)
Incident Response (IR)
Maintenance (MA)
Media Protection (MP)
Physical and Environmental Protection (PE)
Planning (PL)
Personnel Security (PS)
Risk Assessment (RA)
System and Services Acquisition (SA)
System and Communications Protection (SC)
System and Information Integrity (SI).
Program Management (PM)
To aid in selecting controls to meet these requirements, NIST SP 800-53 provides fundamental concepts
and a process for selection and specification of security controls for an information system. Security
controls are organized into classes and families for ease of use in the selection and specification process.
Each family name and unique control identifier corresponds to the above listing of minimum-security
requirements. The families are divided among three classes: management, operational, and technical.
Each security control within a family contains the following information:
Control – describes specific security related activities or actions to be carried out by the organization
or the information system. The control selections often contain assignment and selection options for
customizing a security control.
E-6

Supplemental Guidance – provides additional information related to a specific security control that
should be considered when selecting and implementing security controls.
Control Enhancements – provides statements of security capability to add functionality to or increase
the strength of a basic control.
Implement Security Controls
This activity involves the implementation of security controls in new or legacy information systems. To
help make this process consistent across the Federal government, NIST is currently working to develop
security configuration checklists, which are documented sets of instructions for configuring products to
pre-defined security baselines [27] (e.g., NIST SP 800-68, Guidance for Securing Microsoft Windows XP
Systems for IT Professionals: A NIST Security Configuration Checklist).
Assess Security Controls
This activity determines the extent to which the security controls in the information system are effective
in their application. NIST SP 800-53A provides guidance for assessing security controls initially selected
from NIST SP 800-53 to ensure they are implemented correctly, operating as intended, and producing the
desired outcome with respect to meeting the security requirements of the system. To accomplish this, the
document provides expectations based on assurance requirements defined in NIST SP 800-53 for
characterizing the expectations of security assessments by FIPS 199 impact level. NIST SP 800-53A also
supports:
FISMA annual assessments for major information systems
Security certifications as part of formal system certification and accreditation processes
Continuous monitoring of selected security controls
Preparation for an audit
Identification of resource needs to improve the system’s security posture
Authorize Information System
This activity results in a management decision to authorize the operation of an information system and to
explicitly accept the risk to agency operations, agency assets, or individuals based on the implementation
of an agreed-upon set of security controls.
Monitor Security Controls
This activity continuously tracks changes to the information system that may affect security controls and
assesses control effectiveness. NIST SP 800-37 provides guidance on continuous monitoring.
E-7

Guidance on the Application of Security Controls to ICS
Because today’s ICS are often a combination of legacy systems, often with a planned life span of twenty
to thirty years, or a hybrid of legacy systems augmented with newer hardware and software that are
interconnected to other systems, it is often difficult or infeasible to apply some of the security controls
contained in NIST SP 800-53. Recognizing this problem, NIST created the Industrial Control System
Security project27
in cooperation with the public and private sector ICS community to develop specific
guidance on the application of the security controls in NIST SP 800-53 to ICS.
While most controls in Appendix F of NIST SP 800-53 are applicable to ICS as written, several controls
did require ICS-specific interpretation and/or augmentation by adding one or more of the following to the
control:
ICS Supplemental Guidance provides organizations with additional information on the
application of the security controls and control enhancements in Appendix F of NIST SP 800-
53 to ICS and the environments in which these specialized systems operate. The Supplemental
Guidance also provides information as to why a particular security control or control
enhancement may not be applicable in some ICS environments and may be a candidate for
tailoring (i.e., the application of scoping guidance and/or compensating controls). ICS
Supplemental Guidance does not replace the original Supplemental Guidance in Appendix F of
NIST SP 800-53.
ICS Enhancements (one or more) that provide enhancement augmentations to the original
control that may be required for some ICS
ICS Enhancement Supplemental Guidance that provides guidance on how the control
enhancement applies, or does not apply, in ICS environments.
This ICS-specific guidance is included in NIST SP 800-53, Revision 3, Appendix I: Industrial Control
Systems – Security Controls, Enhancements, and Supplemental Guidance. Section 6 of this document
also provides initial guidance on how 800-53 security controls apply to ICS. Initial recommendations and
guidance, if available, are provided in an outlined box for each section. NIST is planning a December
2011 update to NIST SP 800-53 (NIST SP 800-53, Revision 4), including an update of current security
controls, control enhancements, supplemental guidance, as well as tailoring and supplementation
guidance, in the area of industrial control systems.
In addition, NIST recommends that ICS owners take advantage of the ability to tailor the initial baselines
when it is not possible or feasible to implement specific security controls contained in the baselines.
However, all tailoring activity should, as its primary goal, focus on meeting the intent of the original
security controls whenever possible or feasible.
In situations where the ICS cannot support, or the organization determines it is not advisable to
implement particular security controls or control enhancements in an ICS (e.g., performance, safety, or
reliability are adversely impacted), the organization provides a complete and convincing rationale for how
the selected compensating controls provide an equivalent security capability or level of protection for the
ICS and why the related baseline security controls could not be employed.
If the ICS cannot support the use of automated mechanisms, the organization employs nonautomated
mechanisms or procedures as compensating controls in accordance with the general tailoring guidance in
Section 3.3 of NIST SP 800-53.
Compensating controls are not exceptions or waivers to the baseline controls; rather, they are alternative
safeguards and countermeasures employed within the ICS that accomplish the intent of the original
27
E-8

E-9
security controls that could not be effectively employed. Organizational decisions on the use of
compensating controls are documented in the security plan for the ICS.
To facilitate the understanding of applying NIST SP 800-53 to ICS, a series of ICS cyber security case
histories using actual ICS cyber security incidents, has been developed. These case histories examine the
NIST SP 800-53 ICS controls that were violated or not implemented, and postulate the potential
mitigations that may have occurred if the controls had been implemented. Please visit the project website
for the current releases of these documents.

Appendix F—References
[1] Frazer, Roy, Process Measurement and Control – Introduction to Sensors, Communication
Adjustment, and Control, Prentice-Hall, Inc., 2001.
[2] Falco, Joe, et al., IT Security for Industrial Control Systems, NIST IR 6859, 2003,
http://www.isd.mel.nist.gov/documents/falco/ITSecurityProcess.pdf.
[3] Bailey, David, and Wright, Edwin, Practical SCADA for Industry, IDC Technologies, 2003.
[4] Boyer, Stuart, SCADA Supervisory Control and Data Acquisition, 2nd
Edition, ISA, 1999.
[5] AGA-12, Cryptographic Protection of SCADA Communications, Part 1: Background, Policies and
Test Plan, September, 2005,
http://www.awwarf.org/research/TopicsAndProjects/Resources/SpecialReports/2969/AGAPart1.pdf.
[6] Erickson, Kelvin, and Hedrick, John, Plant Wide Process Control, Wiley & Sons, 1999.
[7] Berge, Jonas, Fieldbuses for Process Control: Engineering, Operation, and Maintenance, ISA,
2002.
[8] Peerenboom, James, Analyzing Infrastructure Interdependencies: Overview of Concepts and
Terminology, Argonne National Laboratory,
http://www.computer.org/portal/web/csdl/doi/10.1109/HICSS.2007.78.
[9] Rinaldi, et al., Identifying, Understanding, and Analyzing Critical Infrastructure Interdependencies,
IEEE Control Systems Magazine, 2001, http://www.ce.cmu.edu/~hsm/im2004/readings/CII-
Rinaldi.pdf.
[10] GAO-04-354, Critical Infrastructure Protection: Challenges and Efforts to Secure Control Systems,
U.S. GAO, 2004, http://www.gao.gov/new.items/d04354.pdf.
[11] Weiss, Joseph, “Current Status of Cyber Security of Control Systems”, Presentation to Georgia Tech
Protective Relay Conference, May 8, 2003.
[12] Keeney, Michelle et al., Insider Threat Study: Computer System Sabotage in Critical Infrastructure
Sectors, United States Secret Service and Carnegie Mellon Software Institute, 2005,
http://www.cert.org/archive/pdf/insidercross051105.pdf.
[13] Federal Information Security Management Act of 2002, Section 301: Information Security,
http://csrc.nist.gov/drivers/documents/FISMA-final.pdf.
[14] Federal Information Security Management Act Implementation Project,
http://csrc.nist.gov/groups/SMA/fisma/index.html.
[15] Federal Information Processing Standards Publication: FIPS 199, Standards for Security
Categorization of Federal Information Systems, NIST, 2004,
http://csrc.nist.gov/publications/fips/fips199/FIPS-PUB-199-final.pdf.
F-1

[16] Federal Information Processing Standards Publication: FIPS 200, Minimum Security Requirements
for Federal Information Systems, NIST, 2006, http://csrc.nist.gov/publications/fips/fips200/FIPS-
200-final-march.pdf.
[17] Swanson, Marianne, et al., NIST SP 800-18, Guide for Developing Security Plans for Federal
Information Systems, Revision 1, 2006, http://csrc.nist.gov/publications/PubsSPs.html.
[18] Swanson, Marianne, NIST SP 800-26, Security Self-Assessment Guide for Information Technology
Systems, 2001, http://csrc.nist.gov/publications/PubsSPs.html.
[19] Ross, Ron, et al., NIST SP 800-39, Managing Information Security Risk, 2011,
http://csrc.nist.gov/publications/PubsSPs.html.
[20] Ross, Ron, et al., NIST SP 800-37, Revision 1, Guide for Applying the Risk Management Framework
to Federal Information Systems, 2010, http://csrc.nist.gov/publications/PubsSPs.html.
[21] Ross, Ron, et al., NIST SP 800-53, Revision 3, Recommended Security Controls for Federal
Information Systems and Organizations, 2010, http://csrc.nist.gov/publications/PubsSPs.html.
[22] Ross, Ron, et al., NIST SP 800-53A, Revision 1,Guide for Assessing the Security Controls in
Federal Information Systems and Organizations, Building Effective Security Assessment Plans,
2010, http://csrc.nist.gov/publications/PubsSPs.html.
[23] Barker, William, NIST SP 800-59, Guideline for Identifying an Information System as a National
Security System, 2003, http://csrc.nist.gov/publications/PubsSPs.html.
[24] Barker, William, NIST SP 800-60, Revision 1, Guide for Mapping Types of Information and
Information systems to Security Categories, 2008, http://csrc.nist.gov/publications/PubsSPs.html.
[25] Souppaya, Murugiah, et al., NIST SP 800-70, Revision 1, Security Configuration Checklists
Program for IT Products – Guidance for Checklists Users and Developers, 2005,
[26] Bowen, Pauline, et al., NIST SP 800-100, Information Security Handbook: A Guide for Managers,
[27] NIST Security Configurations Checklists Program for IT Products, http://checklists.nist.gov/
[28] Stamp, Jason, et al., Common Vulnerabilities in Critical Infrastructure Control Systems, Sandia
National Laboratories, 2003,
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[29] SCADA Security - Advice for CEOs, IT Security Expert Advisory Group (ITSEAG),
http://www.ag.gov.au/agd/WWW/rwpattach.nsf/VAP/(930C12A9101F61D43493D44C70E84EAA)
~SCADA+Security.pdf/$file/SCADA+Security.pdf
[30] Franz, Matthew, Vulnerability Testing of Industrial Network Devices, Critical Infrastructure
Assurance Group, Cisco Systems, 2003, http://blogfranz.googlecode.com/files/franz-isa-device-
testing-oct03.pdf
F-2

[31] Duggan, David, et al., Penetration Testing of Industrial Control Systems, Sandia National
Laboratories, Report No SAND2005-2846P, 2005,
http://www.sandia.gov/scada/documents/sand_2005_2846p.pdf.
[32] 21 Steps to Improve Cyber Security of SCADA Networks, Office of Energy Assurance, U.S.
Department of Energy, http://www.oe.netl.doe.gov/docs/prepare/21stepsbooklet.pdf.
[33] ISA-TR99.03.01: Security Technologies for Industrial Automation and Control Systems, ISA, 2007.
[34] NISCC Good Practice Guide on Firewall Deployment for SCADA and Process Control Networks,
National Infrastructure Security Coordination Centre, London, 2005,
http://www.cpni.gov.uk/docs/re-20050223-00157.pdf.
[35] Idaho National Laboratory, Control Systems Cyber Security: Defense in Depth Strategies, Homeland
Security External Report # INL/EXT-06-11478, May 2006,
http://csrp.inl.gov/Documents/Defense%20in%20Depth%20Strategies.pdf
[36] The IAONA Handbook for Network Security – Draft/RFC v0.4, Industrial Automation Open
Networking Association (IAONA), Magdeburg, Germany, 2003.
[37] Idaho National Laboratory, Common Control System Vulnerability, Homeland Security External
Report # INL/EXT-05-00993, November 2005, www.us-cert.gov/control_systems/pdf/csvul1105.pdf
[38] NIST SP 800-12, An Introduction to Computer Security: The NIST Handbook, 1995,
[39] Mell, Peter, et al., NIST SP 800-40 Version 2, Creating a Patch and Vulnerability Management
Program, 2005, http://csrc.nist.gov/publications/PubsSPs.html.
[40] Scarfone, Karen, et al., NIST SP 800-115, Technical Guide to Information Security Testing and
Assessment, 2008, http://csrc.nist.gov/publications/PubsSPs.html.
[41] Roback, Edward, NIST SP 800-23, Guidelines to Federal Organizations on Security Assurance and
Acquisition/ Use of Tested/Evaluated Products, 2000, http://csrc.nist.gov/publications/PubsSPs.html.
[42] Stoneburner, Gary, et al., NIST SP 800-27, Engineering Principles for Information Security (A
Baseline for Achieving Security), Revision A, 2004, http://csrc.nist.gov/publications/PubsSPs.html.
[43] Grance, Tim, et al., NIST SP 800-35, Guide to Information Technology Security Services, 2003,
[44] Grance, Tim, et al., NIST SP 800-36, Guide to Selecting Information Technology Security Products,
[45] Grance, Tim, et al., NIST SP 800-64, Security Considerations in the Information System
Development Life Cycle, Revision 2, 2008, http://csrc.nist.gov/publications/PubsSPs.html.
[46] Hash, Joan, et al., NIST SP 800-65, Integrating IT Security into the Capital Planning and Investment
Control Process, 2005, http://csrc.nist.gov/publications/PubsSPs.html.
[47] SCADA and Control Systems Procurement Project, http://www.msisac.org/scada/
F-3

[48] Dray, James, et al., NIST SP 800-73-2, Interfaces for Personal Identity Verification, 2008,
[49] Wilson, Charles, et al., NIST SP 800-76, Biometric Data Specification for Personal Identity
Verification, 2007, http://csrc.nist.gov/publications/PubsSPs.html.
[50] Kuhn, D. Richard, et al., NIST SP 800-46, Security for Telecommuting and Broadband
Communications, 2002, http://csrc.nist.gov/publications/PubsSPs.html.
[51] Swanson, Marianne, et al., NIST SP 800-34, Contingency Planning Guide for Information
Technology Systems, 2002, http://csrc.nist.gov/publications/PubsSPs.html.
[52] Burr, William, et al., NIST SP 800-63, Electronic Authentication Guideline, 2006,
[53] Bace, Rebecca, and Mell, Peter, NIST SP 800-31, Intrusion Detection Systems, 2001,
[54] Scarfone, Karen, and Mell, Peter, NIST SP 800-94, Guide to Intrusion Detection and Prevention
Systems (IDPS), 2007, http://csrc.nist.gov/publications/PubsSPs.html.
[55] Falco, Joe, et al., Using Host-based Anti-virus Software on Industrial Control Systems: Integration
Guidance and a Test Methodology for Assessing Performance Impacts, NIST SP 1058, 2006, ,
http://www.nist.gov/manuscript-publication-search.cfm?pub_id=823596.
[56] Peterson, Dale, Intrusion Detection and Cyber Security Monitoring of SCADA and DCS Networks,
ISA, 2004,
http://whitepapers.techrepublic.com.com/whitepaper.aspx?&docid=126355&promo=100511.
[57] Symantec Expands SCADA Protection for Electric Utilities,
http://www.symantec.com/about/news/release/article.jsp?prid=20050914_01
[58] Grance, Tim, et al., NIST SP 800-61, Computer Security Incident Handling Guide, 2004,
[59] Mell, Peter, et al., NIST SP 800-83, Guide to Malware Incident Prevention and Handling, 2005,
[60] Wilson, Mark, and Hash, Joan, NIST SP 800-50, Building an Information Technology Security
Awareness and Training Program, 2003, http://csrc.nist.gov/publications/PubsSPs.html.
[61] Mix, S., Supervisory Control and Data Acquisition (SCADA) Systems Security Guide, EPRI, 2003.
[62] Karygiannis, Tom, and Owens, Les, NIST SP 800-48, Wireless Network Security, 802.11, Bluetooth
and Handheld Devices, 2002, http://csrc.nist.gov/publications/PubsSPs.html.
[63] Frankel, Sheila, et al, NIST SP 800-97, Guide to IEEE 802.11i: Establishing Robust Security
Networks, 2006, http://csrc.nist.gov/publications/PubsSPs.html.
[64] Federal Information Processing Standards Publication: FIPS 201-1, Personal Identity Verification
(PIV) of Federal Employees and Contractors, NIST, 2006,
F-4

F-5
[65] Dray, James, et al, NIST SP 800-96, PIV Card to Reader Interoperability Guidelines, 2006,
[66] Polk, W., Timothy, et al, NIST SP 800-78, Cryptographic Algorithms and Key Sizes for Personal
Identity Verification, 2007, http://csrc.nist.gov/publications/PubsSPs.html.
[67] Souppaya, Murugiah, Kent, Karen, NIST SP 800-92, Guide to Computer Security Log Management,
[68] Jansen, Wayne, NIST SP 800-28, Guidelines on Active Content and Mobile Code, 2001,
[69] Chernick, Michael, et al, NIST SP 800-52, Guidelines for the Selection and Use of Transport Layer
Security (TLS) Implementations, 2005, http://csrc.nist.gov/publications/PubsSPs.html.
[70] Barker, Elaine, et al., NIST SP 800-56A, Recommendation for Pair-Wise Key Establishment
Schemes Using Discrete Logarithm Cryptography, 2007,
[71] Baker, Elaine, et al., NIST SP 800-57, Recommendation for Key Management, 2006,
Part 1, General: http://csrc.nist.gov/publications/PubsSPs.html, Part 2, Best Practices:
[72] Kuhn, D. Richard, et al., NIST SP 800-58, Security Recommendations for Voice Over IP Systems,
[73] Frankel, Sheila, et al, NIST SP 800-77, Guide to IPsec VPNs, 2005,
[74] Internet Security Glossary: RFC 4949, http://www.rfc-editor.org/rfc/rfc4949.txt.
[75] Franz, Matthew, and Pothamsetty, Venkat, ModbusFW Deep Packet Inspection for Industrial
Ethernet, Critical Infrastructure Assurance Group, Cisco Systems, 2004,
http://blogfranz.googlecode.com/files/franz-niscc-modbusfw-may04.pdf.
[76] Duggan, David, Penetration Testing of Industrial Control Systems, Report SAND2005-2846P,
Sandia National Laboratories, 2005, http://www.sandia.gov/scada/documents/sand_2005_2846p.pdf.
[77] Kissel, Richard, et al., NIST SP 800-88, Guidelines for Media Sanitization, 2006,

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