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Rule:
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Sid:
119-2
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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 evade an IDS.
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Detailed Information:
This event is generated when double encoded characters are detected in
web traffic. This is abnormal behavior and may be an indicator of a
possible attack against a vulnerable system.
This may also be an attempt to evade IDS.
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Affected Systems:
Microsoft IIS Servers.
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Attack Scenarios:
An attacker might double encode the request to the web server, this may
then evade an IDS monitoring traffic and could then launch a successful
attack without being detected.
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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.
Upgrade to the latest non-affected version of the software
Use Apache.
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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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