111-15.txt

snort入侵检测规则文件2.4 Snort是众所周知的网络入侵检测工具

Rule: 

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Sid: 
111-15

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Summary: 
This event is generated when the pre-processor stream4
detects network traffic that may constitute an attack.

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Impact: 
Unknown. Possible attempt to evade an IDS.

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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.

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Affected Systems:
	All systems

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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.

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Ease of Attack: 
Simple. Tools such as fragroute enable an attacker to do this.

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False Positives:
None Known.

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False Negatives:
None Known.

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Corrective Action:
Check the target host for signs of compromise.

Ensure the system is up to date with any appropriate vendor supplied patches.

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Contributors:
Martin Roesch <[e-mail]>
Sourcefire Vulnerability Research Team
Nigel Houghton <[e-mail]>

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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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