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Figure 10-4: Intrusion Detection Systems (IDSs)

HOST IDSs

Protocol Stack Monitor (like NIDS)

Collects the same type of information as a NIDS

Collects data even if host is in NIDS blind spot

Gives data specific to hosts; relevant for diagnosis

Might see data after decryption

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Figure 10-4: Intrusion Detection Systems (IDSs)

HOST IDSs

Operating System Monitors

Collect data on operating system events

Failed logins

Attempt to change system executables

Attempt to change system configuration (registry keys, etc.)

3

Figure 10-4: Intrusion Detection Systems (IDSs)

HOST IDSs

Application Monitors (Monitor Specific Applications)

What users did in terms relevant to an application for easy interpretation

Filtering input data for buffer overflows

Signatures of application-specific attacks

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Figure 10-4: Intrusion Detection Systems (IDSs)

Recap

Protocol monitor

Protocol events (suspicious packets, etc.)

Operating monitor

Operating system events (file changes, etc.)

Application monitor

Application events (application commands issued)

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Figure 10-4: Intrusion Detection Systems (IDSs)

HOST IDSs

Weaknesses of Host IDSs

Limited Viewpoint; Only see events on one host

If host is hacked, Host IDS can be attacked and disabled

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Figure 10-4: Intrusion Detection Systems (IDSs)

HOST IDSs Other host-based tools

File integrity checker programs

Create baseline message digests for sensitive files

After an attack, recompute message digests

This tells which files were changed; indicates Trojan horses, etc.

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Figure 10-4: Intrusion Detection Systems (IDSs)

HOST IDSs

Other host-based tools

Operating system lockdown tools

Limits changes possible during attacks

Limits who may make crucial changes

May interfere with software functioning

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Figure 10-4: Intrusion Detection Systems (IDSs)

Log Files

Flat files of time-stamped events

Individual logs

Integrated logs Aggregation of event logs from multiple IDS agents

(Figure 10-7)

Difficult to create because of format incompatibilities

Time synchronization of IDS event logs is crucial (NTP)

Can see suspicious patterns in a series of events across multiple devices

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Figure 10-7: Event Correlation for an Integrated Log File

Sample Log File(Many Irrelevant Log Entries Not Shown)

1. 8:45:05. Packet from 1.15.3.6 to 60.3.4.5 (network IDS log entry)

2. 8:45:07. Host 60.3.4.5. Failed login attempt for account Lee(Host 60.3.4.5 log entry)

3. 8:45:08. Packet from 60.3.4.5 to 1.15.3.6 (network IDS log entry)

4. 8:49:10. Packet from 1.15.3.6 to 60.3.4.5 (network IDS log entry)

5. 8:49:12. Host 60.3.4.5. Failed login attempt for account Lee(Host 60.3.4.5 log entry)

ExternalHost

InternalHost

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Figure 10-7: Event Correlation for an Integrated Log File

Sample Log File(Many Irrelevant Log Entries Not Shown)

6. 8:49:13. Packet from 60.3.4.5 to 1.15.3.6 (network IDS log entry)7. 8:52:07. Packet from 1.15.3.6 to 60.3.4.5 (network IDS log entry) 8. 8:52:09. Host 60.3.4.5. Successful login attempt for account Lee

(Host 60.3.4.5 log entry)

9. 8:52:10. Packet from 60.3.4.5 to 1.15.3.6 (network IDS log entry)10. 8:56:12. Packet from 60.3.4.5 to 123.28.5.210. TFTP request

(network IDS log entry) 11. (no corresponding host log entry)12. 8:56:28. Series of packets from 123.28.5.210 to 60.3.4.5.

TFTP response (network IDS)13. (no more host log entries)

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Figure 10-7: Event Correlation for an Integrated Log File

Sample Log File(Many Irrelevant Log Entries Not Shown)

14. 9:03:17. Packet from 60.3.4.5 to 1.17.8.40. SMTP (network IDS)

15. 9:06:12. Packet from 60.3.4.5 to 1.40.22.8. SMTP (network IDS)

16. 9:10:12. Packet from 60.3.4.5 to 60.0.1.1. TCP SYN=1, Destination Port 80 (network IDS)

17. 9:10:13: Packet from 60.3.4.5 to 60.0.1.2. TCP SYN=1,Destination Port 80 (network IDS)

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Figure 10-4: Intrusion Detection Systems (IDSs)

Analysis Methods

Static packet filtering

Stateful filtering

Full protocol decoding (filters based upon stage in dialogue—login, etc.)

Statistical analysis (frequency thresholds for reporting)

Anomaly detection (compares normal and current operation)

Creates many false positives