GEN:SID 1:1200
Message ATTACK-RESPONSES Invalid URL
Summary This event is generated when an invalid URL response is sent from a
webserver to a client.
Impact Information gathering and possible Denial of Service (DoS).
Detailed Information This event is generated when an invalid URL response is sent from a
webserver to a client. It is possible under some circumstances, to cause
a DoS condition by supplying an invalid URL to a web server running an
affected version of Microsoft IIS 4.0. Certain invalid URLs can cause
the system to make an invalid memory request that will in turn stop the
IIS service from running.
Affected Systems Microsoft IIS 4.0 on NT systems
    
Attack Scenarios The attacker would merely need to make a web request using an invalid
URL.
Ease of Attack Simple. No exploit software required.
Corrective Action Upgrade the system to the latest non-affected version of the software.

Apply the appropriate vendor supplied patches.
Additional References  
Rule References url: www.microsoft.com/technet/security/bulletin/MS00-063.mspx