Microsoft Security Bulletin (MS00-018

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Microsoft Security Bulletin (MS00-018)
- --------------------------------------

Patch Available for "Chunked Encoding Post" Vulnerability

Originally Posted: March 20, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Internet Information Server 4.0. The
vulnerability could allow a malicious user to consume all resources on
a web server and prevent it from servicing other users.

Frequently asked questions regarding this vulnerability can be found
at
http://www.microsoft.com/technet/security/bulletin/fq00-018.asp.

Issue
=====
IIS 4.0 supports chunked encoding transfers, but does not limit the
size of the buffer that can be reserved. This would allow a malicious
user to request an extremely large buffer for a POST or PUT operation,
but never actually send data, thereby blocking memory on the server
that had been allocated to the session. If sufficient memory on the
server were blocked in this fashion, it could prevent the server from
performing useful work. There is no capability through this attack to
create, modify or delete data on the server, nor is there any
capability to usurp administrative control of the server. If the
malicious user closed his session, the memory would be released and
the server's operation would return to normal. Otherwise, the machine
could be put back into normal service by stopping and restarting the
service.

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

Patch Availability
==================
 - X86:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=19761
 - Alpha:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=19762

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.
 - Microsoft Security Bulletin MS00-018: Frequently Asked Questions,
   http://www.microsoft.com/technet/Security/Bulletin/ms00-018.asp.
 - Microsoft Knowledge Base (KB) article Q252693,
   Chunked Encoding Request with No Data Causes IIS Memory Leak,
   http://www.microsoft.com/technet/support/kb.asp?ID=252693.
 - RFC 2616,
   Hypertext Transfer Protocol - HTTP 1.1 ,
   http://www.ietf.org/rfc/rfc2616.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 Petteri Stenius for reporting this issue to us and
working with us to protect customers.

Revisions
=========
 - March 20, 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.

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

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