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Update: Microsoft Security Bulletin (MS00-086)
From: Microsoft Product Security <secnotif () MICROSOFT COM>
Date: Tue, 21 Nov 2000 18:55:39 -0800
The following is a Security Bulletin from the Microsoft Product Security
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Microsoft Security Bulletin (MS00-086)
Patch Available for "Web Server File Request Parsing" Vulnerability
Originally posted: November 06, 2000
Updated: November 21, 2000
On November 06, 2000, Microsoft released the original version of this
bulletin, announcing the availability of a patch that eliminates a
security vulnerability in Microsoft(r) Internet Information Services
5.0. The vulnerability could enable a malicious user to run
operating system commands on a web server. On November 10, 2000, we
updated the bulletin to clarify the scope of the issue. On November
21, 2000, we updated it again, to discuss two newly-discovered
variants of the original vulnerability.
The new variants don't change the effect of exploiting the
vulnerability. However, they do affect a larger number of products.
The original variant affected IIS 5.0 in all cases, but only affected
IIS 4.0 when a service pack prior to Windows NT 4.0 Service Pack 6a
was in use. The new variants affect both IIS 4.0 and IIS 5.0
regardless of the service pack is in use. Microsoft recommends that
all affected customers apply the new versions of the patches.
Frequently asked questions regarding this vulnerability
and the patch can be found at
When IIS receives a valid request for an executable file, it passes
the name of the requested file to the underlying operating system
for processing. However, due to an implementation flaw, it is
possible to create a specially-malformed file request that contains
both a file name and one or more operating system commands. Upon
receiving such a request, IIS would pass the entire string to the
operating system, which would first process the file and then execute
The ability to execute operating system commands on the web server
would enable a malicious user to take virtually any action that an
interactively-logged on user could take. Although this would not give
the malicious user administrative control over the server, it would
nevertheless enable him to cause widespread damage. He could, for
instance, add, delete or change files on the server, run code that
was already on the server, or upload code of his choice and run it.
There are three signficant restrictions on type of file request that
could be used to exploit this vulnerability:
- The malicious user would need to request a .bat or .cmd file.
- The file would need to exist.
- The malicious user would need to have execute permissions on
Although these restrictions limit the scope of the vulnerability, it
is important not to discount it. Many third-party software products
for web servers install batch files by default. As a result,
Microsoft recommends that all customers running affected versions of
IIS verify whether their systems contain any .bat or .cmd files that
can be executed by visitors to the site, and apply the patch
immediately if this is the case. The patch for this issue also
eliminates the "Web Server Directory Traversal" vulnerability
discussed in Microsoft Security Bulletin MS00-078.
Affected Software Versions
- Microsoft Internet Information Server 4.0
- Microsoft Internet Information Services 5.0
- Internet Information Server 4.0:
- Internet Information Services 5.0:
Note: The IIS 5.0 patch can be applied atop systems running either
Windows 2000 Gold or Service Pack 1. It will be included in Windows
2000 Service Pack 2.
Note: The IIS 4.0 patch can be applied atop systems running Windows
NT 4.0 Service Pack 6a. It will be included in Windows NT 4.0
Service Pack 7.
Note: Additional security patches are available at the Microsoft
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-086,
- Microsoft Knowledge Base (KB) article Q277873,
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Product Support Services is available at
Microsoft thanks NSFocus (http://www.nsfocus.com) for reporting the
original and new variants of this vulnerability to us and working
with us to protect customers.
- November 06, 2000: Bulletin Created.
- November 10, 2000: Bulletin updated to indicate that IIS 4.0
is affected when running on pre-SP6 versions of Windows NT 4.0,
and to provide information on additional restrictions on the
- November 21, 2000: Bulletin updated to discuss availability of
that addresses new variants of vulnerability.
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WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
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SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY
DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
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SO THE FOREGOING LIMITATION MAY NOT APPLY.
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- Update: Microsoft Security Bulletin (MS00-086) Microsoft Product Security (Nov 24)