Rule: 

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Sid: 
119-5

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

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Impact: 
Unknown. This may be an attempt to obfuscate an attack an evade an IDS.

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Detailed Information:
This event is generated when the pre-processor http_inspect detects
base36 encoded characters in a web request. This may be used in an
attempt to obfuscate an attack against a webserver or to evade an IDS.

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Affected Systems:
	Microsoft IIS web servers (Asian)

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Attack Scenarios: 
An attacker need only encode a web request using base 36 encoding.

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Ease of Attack: 
Simple. Exploits exist

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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.

Apply any appropriate vendor supplied patches.

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Contributors:
Daniel Roelker <droelker@sourcefire.com> 
Sourcefire Vulnerability Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>

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Additional References:

HTTP IDS Evasions Revisited - Daniel Roelker
http://docs.idsresearch.org/http_ids_evasions.pdf

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