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Intrusion Detection
Chapter 12
Learning Objectives
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Explain what intrusion detection systems
are and identify some major characteristics
of intrusion detection products
Detail the differences between host-based
and network-based intrusion detection
Identify active detection and passive
detection features of both host- and
network-based IDS products
continued…
Learning Objectives
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Explain what honeypots are and how they
are employed to increase network security
Clarify the role of security incident
response teams in the organization
Intrusion Detection System (IDS)
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Detects malicious activity in computer
systems
Identifies and stops attacks in progress
 Conducts forensic analysis once attack is
over
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The Value of IDS
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Monitors network resources to detect
intrusions and attacks that were not
stopped by preventative techniques
(firewalls, packet-filtering routers, proxy
servers)
Expands available options to manage risk
from threats and vulnerabilities
Negatives and Positives
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IDS must correctly identify intrusions and
attacks
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False negatives
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True positives
True negatives
IDS missed an attack
False positives
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Benign activity reported as malicious
Dealing with False Negatives and
False Positives
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False negatives
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Obtain more coverage by using a combination
of network-based and host-based IDS
Deploy NICS at multiple strategic locations in
the network
False positives
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Reduce number using the tuning process
Types of IDS
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Network-based (NIDS)
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Monitors network traffic
Provides early warning system for attacks
Host-based (HIDS)
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Monitors activity on host machine
Able to stop compromises while they are in
progress
Network-based IDS
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Uses a dedicated platform for purpose of
monitoring network activity
Analyzes all passing traffic
Sensors have two network connections
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One operates in promiscuous mode to sniff passing
traffic
An administrative NIC sends data such as alerts to a
centralized management system
Most commonly employed form of IDS
NIDS Monitoring and Management
Interfaces
NIDS Architecture
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Place IDS sensors strategically to defend
most valuable assets
Typical locations of IDS sensors
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Just inside the firewall
On the DMZ
On the server farm segment
On network segments connecting mainframe
or midrange hosts
Connecting the Monitoring Interface
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Using Switch Port Analyzer (SPAN)
configurations, or similar switch features
Using hubs in conjunction with switches
Using taps in conjunction with switches
SPAN
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Allows traffic sent or received in one
interface to be copied to another
monitoring interface
Typically used for sniffers or NIDS sensors
How SPAN Works
Limitations of SPAN
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Traffic between hosts on the same segment
is not monitored; only traffic leaving the
segment crosses the monitored link
Switch may offer limited number of SPAN
ports or none at all
Hub
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Device for creating LANs that forward
every packet received to every host on the
LAN
Allows only a single port to be monitored
Using a Hub in a Switched
Infrastructure
Tap
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Fault-tolerant hub-like device used inline
to provide IDS monitoring in switched
network infrastructures
NIDS Signature Types
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Signature-based IDS
Port signature
Header signatures
Network IDS Reactions
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TCP resets
IP session logging
Shunning or blocking
Host-based IDS
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Primarily used to protect only critical servers
Software agent resides on the protected system
Detects intrusions by analyzing logs of operating
systems and applications, resource utilization,
and other system activity
Use of resources can have impact on system
performance
HIDS Method of Operation
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Auditing logs (system logs, event logs, security
logs, syslog)
Monitoring file checksums to identify changes
Elementary network-based signature techniques
including port activity
Intercepting and evaluating requests by
applications for system resources before they are
processed
Monitoring of system processes for suspicious
activity
HIDS Software
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Host wrappers
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Inexpensive and deployable on all machines
Do not provide in-depth, active monitoring
measures of agent-based HIDS products
Agent-based software
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More suited for single purpose servers
HIDS Active Monitoring Capabilities
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Log the event
Alert the administrator
Terminate the user login
Disable the user account
Advantages of Host-based IDS
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Verifies success or failure of attack by
reviewing HIDS log entries
Monitors use and system activities; useful
in forensic analysis of the attack
Protects against attacks that are not
network based
Reacts very quickly to intrusions
continued…
Advantages of Host-based IDS
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Not reliant on particular network
infrastructure; not limited by switched
infrastructures
Installed on protected server itself; requires
no additional hardware to deploy and no
changes to network infrastructure
Passive Detection Systems
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Can take passive action (logging and
alerting) when an attack is identified
Cannot take active actions to stop an attack
in progress
Active Detection Systems
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Have logging, alerting, and recording features of
passive IDS, with additional ability to take action
against offending traffic
Options
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IDS shunning or blocking
TCP reset
Used in networks where IDS administrator has
carefully tuned the sensor’s behavior to minimize
number of false positive alarms
TCP Reset
Signature-based and
Anomaly-based IDS
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Signature detections
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Also know as misuse detection
IDS analyzes information it gathers and compares it to
a database of known attacks, which are identified by
their individual signatures
Anomaly detection
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Baseline is defined to describe normal state of
network or host
Any activity outside baseline is considered to be an
attack
Intrusion Detection Products
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Aladdin Knowledge Systems
Entercept Security Technologies
Cisco Systems, Inc.
Computer Associates International Inc.
CyberSafe Corp.
Cylant Technology
Enterasys Networks Inc.
Internet Security Systems Inc.
Intrusion.com Inc. family of IDS products
continued…
Intrusion Detection Products
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NFR Security
Network-1 Security Solutions
Raytheon Co.
Recourse Technologies
Sanctum Inc.
Snort
Sourcefire, Inc.
Symantec Corp.
TripWire Inc.
Honeypots
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False systems that lure intruders and gather
information on methods and techniques
they use to penetrate networks—by
purposely becoming victims of their
attacks
Simulate unsecured network services
Make forensic process easy for
investigators
Commercial Honeypots
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ManTrap
Specter
Smoke Detector
NetFacade
Open Source Honeypots
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BackOfficer Friendly
BigEye
Deception Toolkit
LaBrea Tarpit
Honeyd
Honeynets
User Mode Linux
Honeypot Deployment
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Goal
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Gather information on hacker techniques,
methodology, and tools
Options
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Conduct research into hacker methods
Detect attacker inside organization’s network
perimeter
Honeypot Design
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Must attract, and avoid tipping off, the
attacker
Must not become a staging ground for
attacking other hosts inside or outside the
firewall
Honeypots, Ethics, and the Law
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Nothing wrong with deceiving an attacker
into thinking that he/she is penetrating an
actual host
Honeypot does not convince one to attack
it; it merely appears to be a vulnerable
target
Doubtful that honeypots could be used as
evidence in court
Incident Response
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Every IDS deployment should include two
documents to answer “what now”
questions
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IDS monitoring policy and procedure
Incident response plan
IDS Monitoring
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Requires well-documented monitoring
procedures that detail actions for specific
alerts
Information Security Incident
Response Team (SIRT)
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Responsible for assigning personnel to
assemble resources required to handle
security incidents
Typical SIRT Objectives
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Determine how incident happened
Establish process for avoiding further
exploitations of the same vulnerability
Avoid escalation and further incidents
Assess impact and damage of the incident
Recover from the incident
continued…
Typical SIRT Objectives
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Update procedures as needed
Determine who was responsible
Involve legal counsel and law enforcement
officials, as appropriate
Chapter Summary
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Two major types of intrusion detection
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Network-based IDS (monitor network traffic)
Host-based IDS (monitor activity on
individual computers)
Honeypots
Incident response