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Microsoft Security Bulletin (MS00-023)
- --------------------------------------

Patch Available for "Myriad Escaped Characters" Vulnerability

Originally Posted: April 12, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Internet Information Server. The
vulnerability could allow a malicious user to slow a web server's
response or prevent it from providing service altogether  for a period
of time.

Frequently asked questions regarding this vulnerability and the
patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-023.asp

Issue
=====
Special characters can be embedded in URLs by use of so-called escaped
character sequences. By providing a  specially-malformed URL with an
extremely large number of escaped characters, a malicious user could
arbitrarily increase the  work factor associated with parsing the
escaped characters, thereby consuming much or all of the CPU
availability on the  server and preventing 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. 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=20292
 - Internet Information Server 5.0
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20286

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 MS00-023,
   http://www.microsoft.com/technet/security/bulletin/fq00-023.asp
 - Microsoft Knowledge Base article Q254142 discusses this issue and
   will be available soon.
 - 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 Vanja Hrustic of the Relay Group for reporting the
"Myriad Escaped Character" vulnerability to us and  working with us to
protect customers.

Revisions
=========
 - April 12, 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 April 12, 2000

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

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