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Rule:
--
Sid:
111-15
--
Summary:
This event is generated when the pre-processor stream4
detects network traffic that may constitute an attack.
--
Impact:
Unknown. Possible attempt to evade an IDS.
--
Detailed Information:
This event is generated whent the pre-processor stream4 detects abnormal
Time To Live (TTL) values in a datastream. This may indicate an attempt
to evade an IDS.
--
Affected Systems:
All systems
--
Attack Scenarios:
An attacker can set the TTL values of all packets to a value so small
that only the IDS will see the packet and it will not get to the target
system.
--
Ease of Attack:
Simple. Tools such as fragroute enable an attacker to do this.
--
False Positives:
None Known.
--
False Negatives:
None Known.
--
Corrective Action:
Check the target host for signs of compromise.
Ensure the system is up to date with any appropriate vendor supplied patches.
--
Contributors:
Martin Roesch <roesch@sourcefire.com>
Sourcefire Vulnerability Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>
--
Additional References:
Insertion, Evasion, and Denial of Service: Eluding Network Intrusion
Detection:
http://www.insecure.org/stf/secnet_ids/secnet_ids.html
--
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