Microsoft Security Bulletin (MS00-090)

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Patch Available for ".ASX Buffer Overrun" and ".WMS Script Execution"
Vulnerabilities

Originally posted: November 22, 2000

Summary

Microsoft has released a patch that eliminates two security
vulnerabilities in Microsoft(r) Windows Media(tm) Player. These
vulnerabilities could potentially enable a malicious user to cause a
program of his choice to run on another user's computer.

Frequently asked questions regarding this vulnerability
and the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-090.asp

Issue

The two vulnerabilities discussed below are unrelated to each other
except by the fact that they both affect Windows Media Player. We
packaged them in a single patch to make it more convenient for
customers to apply. The vulnerabilities are:

• The ".ASX Buffer Overrun" vulnerability. Windows Media
  Player supports the use of Active Stream Redirector (.ASX)
  files to enable users to play streaming media that resides
  on intranet or Internet sites. However, the code that parses
  .ASX files has an unchecked buffer, and this could potentially
  enable a malicious user to run code of his choice on the
  machine of another user. The malicious user could either send
  an affected file to another user and entice her to run or
  preview it, or he could host such a file on a web site and
  cause it to launch automatically whenever a user visited the
  site. The code could take any action on the machine that the
  legitimate user herself could take.
• The ".WMS Script Execution" vulnerability. Windows Media
  Player 7 introduced a feature called "skins", that allows
  customization of the look and feel of Windows Media Player.
  However, a custom skin (.WMS) file could potentially include
  script, which would execute if Windows Media Player was run
  and that skin was selected. A malicious user could either send
  a customized skin containing script to another user and try to
  entice her into using it, or he could host such a file on a web
  site and cause it to launch automatically whenever a user
  visited the site. Because the code would reside on the user's
  local machine, it would be able to execute ActiveX controls,
  including ones not marked "safe for scripting". This would
  enable the code to take any action that can be accomplished
  via an ActiveX control.

Affected Software Versions

• Microsoft Windows Media Player 6.4
• Microsoft Windows Media Player 7

Note: The ".ASX Buffer Overrun" affects Windows Media Player versions
6.4 and 7. The ".WMS Script Execution" affects only Windows Media
Player version 7. The patch installs the correct fix(es) for the
particular version of Windows Media Player in use.

Patch Availability

• Windows Media Player 6.4:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=26069
• Windows Media Player 7:
  http://www.microsoft.com/Downloads/Release.asp?ReleaseID=26067

Note: The fix for this issue also will be available as part of the
next periodic update, scheduled for December 2000.

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 MS00-090,
  http://www.microsoft.com/technet/security/bulletin/fq00-090.asp
• Microsoft Knowledge Base article Q280419 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
Product Support Services is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments

Microsoft thanks the following people:

• AtStake (http://www.atstake.com) for reporting the ".ASX
  Buffer Overrun" issue to us and working with us to protect
  customers.
• GFI (http://gfi.com) for reporting the ".WMS Script Execution"
  vulnerability to us and working with us to protect customers.

Revisions

• November 22, 2000: Bulletin Created.

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