Operating System:

Published:

02 May 2000

Protect yourself against future threats.

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===========================================================================

              AUSCERT External Security Bulletin Redistribution
                             
           ESB-2000.076 -- Microsoft Security Bulletin (MS00-027)
     Patch Available for "Malformed Environment Variable" Vulnerability
                                 03 May 2000

===========================================================================

	AusCERT Security Bulletin Summary
	---------------------------------

Product:		CMD.EXE
Vendor:			Microsoft
Operating System:	MS Windows NT 4.0 Workstation
			MS Windows NT 4.0 Server
			MS Windows NT 4.0 Server, Enterprise Edition
			MS Windows NT 4.0 Server, Terminal Server Edition
			MS Windows 2000 Professional
			MS Windows 2000 Server
			MS Windows 2000 Advanced Server
Platform:		N/A

Impact:			Denial of Service
Access Required:	Existing User

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Microsoft Security Bulletin (MS00-027)
- - --------------------------------------

Patch Available for "Malformed Environment Variable" Vulnerability

Originally Posted: April 20, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Windows NT(r) 4.0 and Windows(r)  2000.
The vulnerability could allow a malicious user to make some or all of
the memory on an affected server unavailable,  potentially slowing or
stopping an affected server's response time.

Frequently asked questions regarding this vulnerability
and the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-027.asp

Issue
=====
CMD.EXE, the command processor for Windows NT 4.0 and Windows 2000,
has an unchecked buffer in part of the code that handles  environment
strings. Although we believe that it could not be exploited to run
arbitrary code, it could be used to mount  denial of service attacks
in certain cases. If a server provides batch or other script files, a
malicious user could  potentially provide arguments that would create
an extremely large environment string and overflow the buffer. This
would  cause the process to fail, and the memory allocated to the
process would not be made available again until a dialogue had  been
cleared on the operator's console. By repeatedly running the batch
file, the malicious user could potentially make some  or all of the
memory on the server temporarily unavailable.

As noted above, Microsoft believes that arbitrary code cannot be made
to execute via this vulnerability. The machines most  likely to be
affected would be web servers, as they are the most likely types of
machines to offer batch files for use by  remote users. However, even
an otherwise-affected web server would not be vulnerable to this
problem if an operator were  present at the console to clear the error
dialogue promptly.

Affected Software Versions
==========================
 - 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 NT 4.0:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20494
 - Windows 2000:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20503

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 MS00-027,
   http://www.microsoft.com/technet/security/bulletin/fq00-027.asp
 - Microsoft Knowledge Base article Q259622 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 David Litchfield of Cerberus Information Security,
Ltd (http://www.cerberus-infosec.co.uk/) for reporting  this issue to
us and working with us to protect customers.

Revisions
=========
 - April 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.

Last updated April 20, 2000

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

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