Unidirectional Network Architectures
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This document discusses how unidirectional security gateways can maximize security and minimize compliance costs for industrial control systems. It argues that firewalls are porous and all firewalls forward attacks, while unidirectional gateways break the bidirectional channel required for most attacks. The document provides several examples of how unidirectional gateways can be applied in industrial environments and claims they provide stronger security than firewalls while also helping to reduce costs associated with NERC CIP compliance standards.
![Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 10
Regional Auditors Weigh In
● Q: Is External Routable Connectivity (ERC) possible through
Unidirectional Security Gateways?
● No.
● No, though auditors would typically seek evidence that validates a
unidirectional claim.
● A Unidirectional Gateway configured to allow outbound traffic
from the ESP but not allow inbound traffic to enter the ESP would
effectively eliminate External Routable Connectivity.
● Q: Is Remote Screen View (RSV) Interactive Remote Access (IRC)?
● No.
● [With RSV] … the user-initiated process to push screen snapshots
through the ESP is originating from within the ESP. By definition,
that does not constitute Interactive Remote Access.](https://image.slidesharecdn.com/finalpresentation-michaelfirstenberg-waterfall-150925193820-lva1-app6891/85/Unidirectional-Network-Architectures-10-320.jpg)
Unidirectional Network Architectures
- 1. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 2015 Maximize Security to Minimize Compliance Costs Michael H Firstenberg, GICSP, GCIH, CISSP Director of Industrial Security Waterfall Security Solutions
- 2. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 2 Firewalls Are Routers With Filters ● 99% of the Internet is hosts, routers and communications links: ● Hosts are sources and destinations of messages ● Routers forward messages through communications links ● Firewalls are routers with filters – the filter looks at each message and decides whether to forward it, or drop it ● No filter is or can ever be perfect All firewalls forward attacks from external networks to protected” networks Hosts Routers
- 3. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 3 Firewall have been with us for 30 years now. The good guys and the bad guys both know how to defeat them. All Firewalls Are Porous Photo: Red Tiger Security Attack Difficulty: Impossible Routine Easy Attack Type UGW Fwall 1) Phishing / drive-by-download – victim pulls your attack through firewall 2) Social engineering – steal a password / keystroke logger / shoulder surf 3) Compromise domain controller – create ICS host or firewall account 4) Attack exposed servers – SQL injection / DOS / buffer-overflow 5) Attack exposed clients – compromised web svrs/ file svrs / buf-overflows 6) Session hijacking – MIM / steal HTTP cookies / command injection 7) Piggy-back on VPN – split tunneling / malware propagation 8) Firewall vulnerabilities – bugs / zero-days / default passwd/ design vulns 9) Errors and omissions – bad fwall rules/configs / IT reaches through fwalls 10) Forge an IP address – firewall rules are IP-based
- 4. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 4 PLCs RTUs Historian Server Workstations Replica Server Waterfall TX agent Waterfall RX agent Corporate NetworkIndustrial Network Unidirectional Historian replication Waterfall TX Module Waterfall RX Module Historian Replication With Unidirectional Gateways ● Hardware-enforced unidirectional server replication ● Replica server contains all data and functionality of original ● Corporate workstations communicate only with replica server ● Industrial network and critical assets are physically inaccessible from corporate network & 100% secure from any online attack
- 5. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 5 Historian Replication With Unidirectional Gateways
- 6. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 6 Waterfall’s Family of Unidirectional Products Product Icon Description Unidirectional Security Gateway Combination of hardware and software that replicates servers out of a control system only – physically impossible to send anything back into the protected network Waterfall FLIP A reversible Unidirectional Security Gateway. Replicates servers in one direction, or the other, but never both at the same time. Inbound/Outbound Gateways One Unidirectional Security Gateway replicating servers in one direction. A second gateway independently replicates a different set of servers in the other direction. Application Data Control Software add-on providing fine-grain, policy-based inspection and control over industrial data flows, even for encrypted, compressed, proprietary and undocumented industrial protocols. Secure Bypass For emergency access to networks during declared CIP emergencies.
- 7. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 7 Typical Unidirectional Use Cases ● Safety systems – replicate Modbus servers and Syslog & SNMP clients ● Protection systems – replicate DNP3 & event log servers ● IT/OT integration – replicate historian & OPC servers and many others ● Optional: FLIP to replicate security updates back in as well ● Generation dispatch – base load replicates ICCP server out ● Peaking plant independently replicates ICCP server in as well ● Turbine vendor – replicate historian & other servers out to turbine vendor. ● Remote Screen View for adjustments At least one layer of unidirectional products breaks chain of attack from Internet through to ICS & protective relays
- 8. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 8 NERC-CIP V5 ● CIP V5 encourages the use of Unidirectional Security Gateways ● External Routable Connectivity: The ability to access a BES Cyber System that is accessible from a Cyber Asset that is outside of its associated Electronic Security Perimeter via a bi-directional routable protocol connection. ● 38 of 129 medium-impact requirements apply only if the affected cyber asset has external routable connectivity “When you are considering security for your control networks, you need to keep in mind innovative security technologies such as unidirectional gateways” Tim Roxey, NERC CSSO
- 9. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 9 CIP Standard Total Requirements ERC-Exempt Med Impact Requirements ERC-Exempt High Impact Requirements 002 BES Cyber System Categorization 7 - - 003 Security Management Controls 4 - - 004 Personnel and Training 19 15 - 005 Electronic Security Perimeters 8 7 5 006 Physical Security of BES Cyber Systems 14 11 - 007 Systems Security Management 20 5 - 008 Incident Reporting & Resp. Planning 9 - - 009 Recovery Plans 10 - - 010 Change Mgmt & Vuln Assessments 10 - - 011 Information Protection 4 - - 014 Physical Security 24 - - Totals: 129 38 5 NERC CIP V5 Details Proposed NERC CIP V6 preserves all of the above, and the new Low Impact External Routable Connectivity (LERC) definition also includes the word “bi-directional”
- 10. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 10 Regional Auditors Weigh In ● Q: Is External Routable Connectivity (ERC) possible through Unidirectional Security Gateways? ● No. ● No, though auditors would typically seek evidence that validates a unidirectional claim. ● A Unidirectional Gateway configured to allow outbound traffic from the ESP but not allow inbound traffic to enter the ESP would effectively eliminate External Routable Connectivity. ● Q: Is Remote Screen View (RSV) Interactive Remote Access (IRC)? ● No. ● [With RSV] … the user-initiated process to push screen snapshots through the ESP is originating from within the ESP. By definition, that does not constitute Interactive Remote Access.
- 11. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 11 CIP V5 Segmentation Entities may choose to segment generating units at a 1500 MW generation resource and their associated BES Cyber Systems such that each segmented unit, or group of units, and their associated BES Cyber Systems do not meet the 1500 MW criteria described in CIP‐002‐5.1, Attachment 1, Criterion 2.1. Segmenting generating units and their associated BES Cyber Systems can reduce risks to the reliable operation of the BES. ● Eliminate / duplicate shared systems, eg: coal feeds, air compressors ● Provide evidence of analysis, that no systems remain able to impact 1500MW or more within 15 minutes ● Demonstrate access restrictions on network interfaces “(eg: firewall rules)” But: firewalls provide only minimal protection to segmented networks. How does this reduce risks to reliable operation of the BES?
- 12. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 12 Secure Segmentation ● Take a tiny fraction of segmentation’s CIP compliance cost savings and apply them to securing segmented DCS networks unidirectionally ● Strong security: ● Breaks one large target into many smaller targets ● Each smaller target is safe from simultaneous / coordinated attack from the Internet or corporate network ● Dramatically reduce cost of risks Unidirectionally protecting segmented units is good business
- 13. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 13 Use Case: Protecting Protection Equipment ● Recloser discipline – need to protection equipment after faults ● Continuous commands to adjust other components ● FLIP separates control equipment from protection equipment ● Relays are continuously monitored & occasionally updated ● All software can be hacked. Relays are software. Protecting relays is essential to prevent damage to equipment How many FLIPs are normal, not suspicious? Relays RTUs FLIP Substation Electronic Security Perimeter Firewall WAN EMS
- 14. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 14 Use Case: Protecting Entire Substation ● Continuous monitoring of substation via DNP3 / IEC 60870-5-104 ● FLIP on demand when commands come through ● FLIP trigger raises alarm if too many FLIPs ● Trigger controller cannot be compromised by network attack How many FLIPs are normal, not suspicious? Relays RTUs Substation Electronic Security Perimeter FLIP WAN EMS
- 15. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 15 Use Case: Continuous Adjustment ● Continuous monitoring of substation via DNP3 / IEC 60870-5-104 ● Continuous command channel ● Separate channels, not command/response ● Unlike firewall, do not forward messages, resists fuzzing & buffer- overflow attacks How many FLIPs are normal, not suspicious? Relays RTUs Substation Electronic Security Perimeter WAN EMS
- 16. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 16 Use Case: In/Out Gateways for Balancing Authority ● BA sends ICCP setpoints to partner utilities every 2 seconds + polls utilities for ICCP data every 2 seconds ● Independent channels – not command/response channels ● Each channel replicates one or more ICCP servers ● Multiply redundant – automatic at site, manual fail-over between sites ● Minimal ICCP reconfiguration needed
- 17. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 17 Inbound + Outbound: Stronger than Firewalls ● Multiple computers/layers of protection must all be compromised, rather than just one layer in the firewall ● TX Agents are clients. They do not forward messages. They ask for data and forward the answers/data ● No protocol-level attacks pass through – no fuzzing/buffer overflows. All communications / TCP / ICCP sessions terminate in agent hosts ● Targeted / persistent attacks are “flying blind” – targeted attack requires insider assistance Inbound / outbound gateways do not forward packets or filter packets, they forward data
- 18. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 18 Attack Modelling ● Quantitative Risk (earthquakes, pandemic) = Likelihood * Cost ● Qualitative Risk (Cyber) = Threat * Vulnerability * Likelihood * Cost ● Qualitative scores mean nothing to senior decision-makers ● Attack modelling – describe attacks, not qualitative risks ● Attack training / expertise is essential to defense ● Design basis threat: what is the simplest attack able to breach our defences with a high degree of confidence No defense is perfect. Attack expertise is essential to evaluating a defensive posture
- 19. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 19 Current Defensive Posture: Design Basis Threat Disable safeties Disable safeties Local misoperation Disable safeties Disable safeties Compromised insider Rem targeted misoperation Remote misoperation Physical Vandalism Remote misoperation Remote misoperation Autonomous malware Rem targeted ransomware Remote shutdown Drop malware Erase hard drives Erase hard drives Sleeper malware Ransomware Vandalism – delete files Remote misoperation Remote shutdown Remote shutdown Remote misoperation Virus triggers shutdown Drop malware Remote shutdown Embarrass Business Sleeper malware Erase hard drives Organized Crime IT Insider ICS Insider Hacktivist Intelligence Agency Military
- 20. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 20 Proposed Upgrade to Next-Gen Firewall – No Change Disable safeties Disable safeties Local misoperation Disable safeties Disable safeties Compromised insider Rem targeted misoperation Remote misoperation Physical Vandalism Remote misoperation Remote misoperation Autonomous malware Rem targeted ransomware Remote shutdown Drop malware Erase hard drives Erase hard drives Sleeper malware Ransomware Vandalism – delete files Remote misoperation Remote shutdown Remote shutdown Remote misoperation Virus triggers shutdown Drop malware Remote shutdown Embarrass Business Sleeper malware Erase hard drives Organized Crime IT Insider ICS Insider Hacktivist Intelligence Agency Military
- 21. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 21 Proposed Upgrade to Unidirectional Security Gateway Disable safeties Disable safeties Local misoperation Disable safeties Disable safeties Compromised insider Rem targeted misoperation Remote misoperation Physical Vandalism Remote misoperation Remote misoperation Autonomous malware Rem targeted ransomware Remote shutdown Drop malware Erase hard drives Erase hard drives Sleeper malware Ransomware Vandalism – delete files Remote misoperation Remote shutdown Remote shutdown Remote misoperation Virus triggers shutdown Drop malware Remote shutdown Embarrass Business Sleeper malware Erase hard drives Organized Crime IT Insider ICS Insider Hacktivist Intelligence Agency Military
- 22. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 22 Evolving Best Practices – Unidirectional Gateways NERC CIP V5 exempts unidirectionally- protected sites from over 30% of requirements DHS recommends unidirectional gateways in security assessments (ICS CERT) Unidirectional gateways – limit the propagation of malicious code (ISA SP- 99-3-3 / IEC 62443-3-3) ENISA - unidirectional gateways provide better protection than firewalls ANSSI Cybersecurity for ICS – many requirements for hardware-enforced unidirectionality NIST – gateways are used in guarantee- ing protection of critical systems (NIST 800-82)
- 23. Proprietary Information -- Copyright © 2015 by Waterfall Security Solutions 23 ● Medium Impact ERC exemptions dramatically reduce CIP V5 costs ● Generating plant segmentation and other uses of Unidirectional Security Gateways and related products dramatically improve security ● Attack modelling makes security benefits of Unidirectional Gateways clear to senior decision-makers ● Net present value modelling makes operating cost of firewalls clear, even excluding CIP program costs NERC CIP program costs are naturally reduced when strong, unidirectional security is deployed For articles & whitepapers to dig deeper on these topics: www.waterfall-security.com Strong Security Is Good Business