File: 111-15.txt

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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

--