Microsoft Security Bulletin (MS00-030)
Patch Available for "Malformed Extension Data in URL" Vulnerability
Originally Posted: May 11, 2000
Microsoft has released a patch that eliminates a security vulnerability in Microsoft(r) Internet Information Server. The vulnerability could be used to slow the performance of an affected server, or temporarily stop it altogether.
Frequently asked questions regarding this vulnerability and the patch can be found at http://www.microsoft.com/technet/security/bulletin/fq00-030.asp
In compliance with RFC 2396, the algorithm in IIS that processes URLs has flexibility built in to allow it to process any arbitrary sequence of file extensions or subresource identifiers (referred to in the RFC as path_segments). By providing an URL that contains specially-malformed file extension information, a malicious user could misuse this flexibility in order to arbitrarily increase the work factor associated with parsing the URL. This could consume much or all of the CPU availability on the server and prevent useful work from being done.
The vulnerability does not provide any capability to cause the server to fail, or to add, change or delete data on it. Likewise, it provides no capability to usurp administrative control of the web server. The slowdown would only last until the URL had been processed, at which point service would return to normal.
Note: Additional security patches are available at the Microsoft Download Center
Please see the following references for more information related to this issue. - Frequently Asked Questions: Microsoft Security Bulletin MS00-030, http://www.microsoft.com/technet/security/bulletin/fq00-030.asp - Microsoft Knowledge Base article Q260205 discusses this issue and will be available soon. - RFC 2396, Uniform Resource Identifiers (URI): Generic Syntax, http://www.ietf.org/rfc/rfc2396.txt. - Microsoft TechNet Security web site, http://www.microsoft.com/technet/security/default.asp
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/support/contact/default.asp.
Microsoft thanks Underground Security Systems Research (http://www.ussrback.com) for reporting this vulnerability to us and working with us to protect customers.
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Last updated May 11, 2000