Rule:

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Sid:
1289

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Summary:
This event is generated when an exploited Internet Information Server (IIS) host attempts to perform a tftp download of the file admin.dll to infect the host with the nimda worm. 

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Impact:
Administrator access.  A successful attack can allow remote execution of commands with administrator privleges.

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Detailed Information:
The nimda worm uses multiple propagation methods.  One method exploits a victim Internet Information Server (IIS) using a unicode directory traversal attack to execute commands on the target server.  An attempt is made to execute a tftp download of the file admin.dll from the infected attacking host to the victim server.  The admin.dll file is a copy of the nimda worm that is activated on the newly infected victim server.  This event is triggered if the IIS server is exploitable and the tftp transfer is attempted.

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Affected Systems:
Hosts running Microsoft IIS 4.0 and 5.0.

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Attack Scenarios:
The worm will attempt to remotely exploit a unicode directory vulnerability to infect an IIS server by executing a tftp download of the nimda worm.

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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:
Apply the appropriate patch referenced in Microsoft Security Bulletin MS00-078.

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Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com> 
Nigel Houghton <nigel.houghton@sourcefire.com>
Judy Novak <judy.novak@sourcefire.com>

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Additional References:

CERT:
http://www.cert.org/advisories/CA-2001-26.html

Microsoft:
http://www.microsoft.com/technet/Security/Bulletin/ms00-078.asp

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