Rule:

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Sid:
517

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Summary:
This event is generated when an attempt is made to query the XDMCP 
service.

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Impact:
Serious. Information disclosure. Unauthorized access to the system.

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Detailed Information:
An XDMCP query can provide a wealth of information about a host such as 
a login screen, a list of users on the host, and to bypass access 
control restrictions used by tcpwrapper and to bypass the restriction of
login by user "root" on the box.

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Affected Systems:
	Any UNIX based server running XDMCP.

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Attack Scenarios:
An attacker can use this to find out information about the machine and 
then either launch a specific attack or connect to the X windows server 
using XDMCP.

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Ease of Attack:
Simple.

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False Positives:
None Known

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False Negatives:
None Known

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Corrective Action:
Disable XDMCP if not needed.

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Contributors:
Original Rule Writer Unknown
Sourcefire Research Team
Nigel Houghton <nigel.houghton@sourcefire.com>
Snort documentation contributed by Josh Sakofsky

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Additional References:

Arachnids:
http://www.whitehats.com/info/IDS476

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