Ch03 Protecting Systems

 At least one in ten web pages are booby-trapped
with malware (link Ch 3a)
 Just viewing an infected Web page installs
malware on your computer, if your operating
system and browser are vulnerable

 Explain how to harden operating systems
 List ways to prevent attacks through a Web
browser
 Define SQL injection and explain how to protect
against it
 Explain how to protect systems from
communications-based attacks
 Describe various software security applications

 Updates to the operating system
 Protecting against buffer overflows
 Configuring operating system protections

 Operating systems are huge and contain many bugs
(errors in code)
 Linux contains 0.17 bug per 1,000 lines of code
 Typical commercial software contains 20-30 bugs per
1,000 lines of code (link Ch 3b)
 81 bugs a day were reported for Windows Vista Beta 2
(link Ch 3c)
 Some of those bugs create vulnerabilities

 Security patch
 A general software security update intended to cover
vulnerabilities that have been discovered
 Hotfix addresses a specific customer situation
 Often may not be distributed outside that customer’s
organization
 Service pack
 A cumulative package of all security updates plus
additional features

 Automatic
Updates
Options
 Patches can
sometimes
create new
problems

 Used to manage patches locally instead of relying
upon the vendor’s online update service
 Advantages
 Administrators can test patches before deploying
them
 Every machine is updated simultaneously
 Users cannot disable or circumvent updates
 Can save bandwidth and time
 Computers that do not have Internet access can
receive updates

 Buffer overflow
 Occurs when a process attempts to store data in
random access memory (RAM) beyond the
boundaries of a fixed-length storage buffer
 Extra data overflows into the adjacent memory
locations and under certain conditions may cause the
computer to stop functioning
 Attackers also use a buffer overflow in order to
compromise a computer

 Basic defenses
 Write “defensive” program code that will protect
against these attacks
 Use a programming language that makes these
attacks more difficult
 For Windows-based systems, there are two
defenses against buffer overflows
 Data execution prevention (DEP)
 Address space layout randomization (ASLR)

 Most modern CPUs support an NX (No
eXecute) bit to designate a part of memory
for containing only data
 DEP will not allow code in the memory area
to be executed
 Windows Vista allows software developers to
enable NX hardware protection specifically
for the application software that they develop

 In Windows 7
 Start, right-click
Computer,
Properties,
Advanced System
Settings, Advanced
Tab, Performance
Settings

 Randomly assigns executable operating system
code to one of 256 possible locations in memory
 This makes it harder for an attacker to locate
and take advantage of any functionality inside
these executables
 ASLR is most effective when it is used in
conjunction with DEP

 Download Process Explorer (link Ch 3e)
 View, Show Lower Pane
 View, Lower Pane View, DLLS
 View, Select Columns, DLL tab, Base Address
 Select explorer.exe and find ntdll.dll
 Reboot to see base address change
 (link Ch 3d)

 Four steps:
 Security policy
 Define defense mechanisms company will use
 Configuration baseline
 Operating System settings
 Security template
 A set of settings in a single package
 Deployment
 Manually or through Group Policy

 Cookies
 JavaScript
 Java
 ActiveX
 Cross-site scripting (XSS)

 Cookies are computer files that contain user-
specific information
 Types of cookies
 First-party cookie
 Third-party cookie
 Cookies can pose a privacy risk
 Cookies can be used to track the browsing or buying
habits of a user
 Defenses against cookies include disabling the
creation of cookies or deleting them once they are
created

 JavaScript
 Developed by Netscape
 Scripting language that does not create standalone
applications
 Scripting language
 A computer programming language that is typically
interpreted into a language the computer can understand
 Visiting a Web site that automatically downloads a
program to run on a local computer can be
dangerous

 Several defense mechanisms prevent JavaScript
programs from causing serious harm:
 JavaScript cannot read or write files
 JavaScript cannot connect to other machines on your
LAN
 Other security concerns remain:
 JavaScript programs can capture and send user
information without the user’s knowledge or
authorization
 The defense against JavaScript is to disable it
within the Web browser

 Java
 A complete object-oriented programming language
created by Sun Microsystems
 Can be used to create standalone applications
 Java applet
 A separate program stored on a Web server and
downloaded onto a user’s computer along with HTML
code
 Can also be made into hostile programs

 Sandbox is a defense against a hostile Java
applet
 Surrounds program and keeps it away from private
data and other resources on a local computer
 Two types of Java applets:
 Unsigned Java applet: program that does not come
from a trusted source
 Signed Java applet: has information proving the
program is from a trusted source and has not been
altered

 Set of technologies developed by Microsoft
 Not a programming language but a set of rules for
how applications should share information
 ActiveX controls
 Also called add-ons or ActiveX applications
 Represent a specific way of implementing ActiveX
 Can perform many of the same functions of a Java applet,
but do not run in a sandbox
 Have full access to Windows operating system
 ActiveX poses a number of security concerns

 Nearly all ActiveX control security mechanisms
are set in Internet Explorer
 ActiveX controls do not rely exclusively on
Internet Explorer
 However, can be installed and executed
independently
 The defense against ActiveX is to disable it
within the Web browser

 Cross Site Scripting (XSS)
 An attack in which malicious code is inserted into a
specific type of dynamic Web page
 Typically involves using client-side scripts written in
JavaScript or ActiveX
 Designed to extract information from the victim and
then pass the information to the attacker
 Targeted to Web sites that dynamically generate
Web pages that redisplay (echo) user input that has
not been properly validated

 Cross Site Scripting (XSS) attack steps
 An attacker searches for a Web site that redisplays a
bad login (See Figures 3-8 and 3-9)
 The attacker then creates an attack URL that
contains the embedded JavaScript commands
 A fake e-mail is sent to unsuspecting users with the
attack URL as a modified embedded link in the e-mail
 The unsuspecting victim clicks on the attack URL and
enters his username and password

 Defenses against XSS involve both Web masters
of legitimate sites as well as users
 Webmasters should check that all user input is
validated and that attackers do not have the ability to
inject code
 They also should be sure that all Web services and
database software is patched to prevent XSS
 Users should never click on embedded links in e-mails

 One of the most common types of attacks
 Uses a form of injection like XSS
 Hinges on an attacker being able to enter an
SQL database query into a dynamic Web page
 SQL (structured query language)
 A language used to view and manipulate data that is
stored in a relational database

 Hackthissite.org
 Don't put anything true about you on this site--
they are real criminals

 Displays entire username database

 Variations to the SQL injection attack
 Deleting data from the database
 Accessing the host operating system through
function calls
 Retrieving a list of all usernames and passwords

 E-mail systems use two TCP/IP protocols to send
and receive messages
 Simple Mail Transfer Protocol (SMTP) handles outgoing
mail
 Post Office Protocol (POP3 for the current version)
handles incoming mail
 IMAP (Internet Mail Access Protocol)
 A more advanced protocol that solves many problems
 E-mail remains on the e-mail server
 Mail can be organized into folders and read from any
computer
 Current version is IMAP4

 SMTP relay
 SMTP servers can forward e-mail sent from an e-mail
client to a remote domain
 SMTP open relay
 If SMTP relay is not controlled, an attacker can use it to
forward thousands of spam e-mail messages
 The defenses against SMTP open relay are to turn
off mail relay altogether
 So that all users send and receive e-mail from the local
SMTP server only or limit relays to only local users

 Instant messaging (IM)
 Real-time communication between two or more
users
 Can also be used to chat between several users
simultaneously, to send and receive files, and to
receive real-time stock quotes and news
 Basic IM has several security vulnerabilities
 IM provides a direct connection to the user’s
computer; attackers can use this connection to
spread viruses and worms
 IM is not encrypted by default so attackers could view
the content of messages

 Steps to secure IM include:
 Keep the IM server within the organization’s firewall
and only permit users to send and receive messages
with trusted internal workers
 Enable IM virus scanning
 Block all IM file transfers
 Encrypt messages

 Peer-to-peer (P2P) network
 Uses a direct connection between users
 Does not have servers, so each device simultaneously
functions as both a client and a server to all other devices
connected to the network
 P2P networks are typically used for connecting
devices on an ad hoc basis
 For file sharing of audio, video, and data, or real-time data
transmission such as telephony traffic
 Viruses, worms, Trojan horses, and spyware can be
sent using P2P

 A new type of P2P network has emerged known
as BitTorrent
 Torrents are active Internet connections that
download a specific file available through a
tracker
 Server program operated by the person or organization
that wants to share the file
 With BitTorrent, files are advertised
 BitTorrent downloads are often illegal and
contain malware

 Antivirus
 Anti-spam
 Popup blockers
 Personal software firewalls
 Host intrusion detection systems

 Antivirus (AV) software
 Scan a computer for infections as well as monitor
computer activity and scan all new documents, such
as e-mail attachments, that might contain a virus
 If a virus is detected, options generally include
cleaning the file of the virus, quarantining the
infected file, or deleting the file
 The drawback of AV software is that it must be
continuously updated to recognize new viruses
 AV software use definition files or signature files

 Popup
 A small Web browser window that appears over the Web
site that is being viewed
 Popup blocker
 Allows the user to limit or block most popups
 Can be either a separate program or a feature
incorporated within a browser
 As a separate program, popup blockers are often
part of a package known as antispyware
 Helps prevent computers from becoming infected by
different types of spyware

 Two different options for installing a corporate
spam filter
 Install the spam filter with the SMTP server
 See Figure 3-14
 Install the spam filter with the POP3 server
 See Figure 3-15

 Another way to filter spam is for the
organization to contract with a third-party entity
 That filters out spam
 All e-mail is directed to the third-party’s remote
spam filter
 Where it is cleansed before it is redirected back to the
organization
 This can be accomplished by changing the MX (mail
exchange) record

 A third method is to filter spam on the local
computer
 Typically, the e-mail client contains several different
features to block spam, such as:
 Level of junk e-mail protection
 Blocked senders
 Allowed senders
 Blocked top level domain list
 A final method of spam filtering is to install separate
filtering software that works with the e-mail client
software

 Very effective
 Free
 Automatic -
effortless to use

 Firewall, sometimes called a packet filter
 Designed to prevent malicious packets from entering
or leaving computers
 Can be software-based or hardware-based
 Personal software firewall
 Runs as a program on a local system to protect it
against attacks
 Many operating systems now come with
personal software firewalls
 Or they can be installed as separate programs

 Monitors network traffic
 Detects and possibly prevents attempts to
 HIDS are software-based and run on a local computer
 These systems can be divided into four groups:
 File system monitors
 Logfile analyzers
 Connection analyzers
 Kernel analyzers
 HIDS compare new behavior against normal
behavior

Ch03 Protecting Systems

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Ch03 Protecting Systems