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From:MICROSOFT <secure_(at)_microsoft.com>
Date:20.05.2000
Subject:Security Bulletin (MS00-029)

Microsoft Security Bulletin (MS00-029)
- --------------------------------------

Patch Available for "IP Fragment Reassembly" Vulnerability

Originally Posted: May 19, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Windows(r) 95, Windows 98, Windows
NT(r) 4.0 and Windows 2000. The vulnerability could be used to cause
an affected machine to temporarily stop performing  useful work.

Frequently asked questions regarding this vulnerability and
the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-029.asp

Issue
=====
The affected systems contain a flaw in the code that performs IP
fragment reassembly. If a continuous stream of fragmented IP
datagrams with a particular malformation were sent to an affected
machine, it could be made to devote most or all of its CPU
availability to processing them. The data rate needed to completely
deny service varies depending on the machine and network  conditions,
but in most cases even relatively moderate rates would suffice.

The vulnerability would not allow a malicious user to compromise data
on the machine or usurp administrative control over it.  Although it
has been reported that the attack in some cases will cause an affected
machine to crash, affected machines in all  Microsoft testing returned
to normal service shortly after the fragments stopped arriving.
Machines protected by a proxy  server or a firewall that drops
fragmented packets would not be affected by this vulnerability. The
machines most likely to  be affected by this vulnerability would be
machines located on the edge of a network such as web servers or proxy
servers.

Affected Software Versions
==========================
- Microsoft Windows 95
- Microsoft Windows 98
- Microsoft Windows NT 4.0 Workstation
- Microsoft Windows NT 4.0 Server
- Microsoft Windows NT 4.0 Server, Enterprise Edition
- Microsoft Windows NT 4.0 Server, Terminal Server Edition
- Microsoft Windows 2000 Professional
- Microsoft Windows 2000 Server
- Microsoft Windows 2000 Advanced Server

Patch Availability
==================
- Windows 95:
  http://download.microsoft.com/download/win95/update/8070/
  w95/EN-US/259728USA5.EXE
- Windows 98:
  http://download.microsoft.com/download/win98/update/8070/
  w98/EN-US/259728USA8.EXE
- Windows NT 4.0 Workstation, Server and Server, Enterprise
  Edition:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20829
- Windows NT 4.0 Server, Terminal Server Edition:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20830
- Windows 2000 Professional, Server and Advanced Server:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20827

Note: Line breaks have been inserted into the URLs above for
readability.

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 MS00-029,
  http://www.microsoft.com/technet/security/bulletin/fq00-029.asp
- Microsoft Knowledge Base article Q259728 discusses this issue
  and will be available soon.
- RFC 791, Internet Protocol,
  http://www.ietf.org/rfc/rfc0791.txt?number=791
- 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 Bindview's RAZOR Security Team
(http://www.bindview.com) for reporting this issue to us and working
with us  to protect customers.

Revisions
=========
- May 19, 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,
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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 19, 2000

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