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Rule:
--
Sid:
119-4
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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:
Microsoft IIS servers are able to use non-ASCII characters as values
when decoding UTF-8 values. This is non-standard behavior for a
webserver and violates RFC recommendations. All non-ASCII values should
be encoded with a %. This event may indicate an attack against a web
server or at the least an attempt to evade an IDS.
No web clients encode UTF-8 characters in this way. This is most likely
a malicious request.
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Affected Systems:
All Microsoft IIS servers
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Attack Scenarios:
An attacker merely needs to encode a web request using this non-standard
format.
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Ease of Attack:
Simple. Many exploits exist.
--
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.
--
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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