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Microsoft Security Bulletin (MS00-030)
- --------------------------------------

Patch Available for "Malformed Extension Data in URL" Vulnerability

Originally Posted: May 11, 2000

Summary
=======
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

Issue
=====
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.

Affected Software Versions
==========================
 - Microsoft Internet Information Server 4.0
 - Microsoft Internet Information Server 5.0

Patch Availability
==================
 - Internet Information Server 4.0:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20906
 - Internet Information Server 5.0:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20904

Note: Additional security patches are available at the Microsoft
Download Center

More Information
================
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

Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments
===============
Microsoft thanks Underground Security Systems Research
(http://www.ussrback.com) for reporting this vulnerability to us and
working with us to protect customers.

Revisions
=========
 - May 11, 2000: Bulletin Created.

- ---------------------------------------------------------

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED
"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT  DISCLAIMS ALL
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR  PURPOSE. IN NO EVENT
SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES
WHATSOEVER INCLUDING DIRECT,  INDIRECT, INCIDENTAL, CONSEQUENTIAL,
LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT
CORPORATION OR ITS  SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF
LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING
LIMITATION MAY NOT APPLY.

Last updated May 11, 2000

(c) 2000 Microsoft Corporation. All rights reserved. Terms of use.

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