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Microsoft Windows Media Player DVR-MS Memory Corruption Vulnerability



Windows Media Player is a video and audio file player for Windows based systems. It supports multiple file formats and allows playing files from either the local filesystem or the network. More information can be at:


Remote exploitation of a memory corruption vulnerability in Microsoft Corp.'s Windows Media Player could allow an attacker to execute arbitrary code with the privileges of the current user.

Microsoft Digital Video Recording (DVR-MS) is a proprietary video and audio file container format which can be used with Windows Media Player. A vulnerability exists in the Windows Media Player XDS Codec filter during the processing of a specially crafted DVR-MS file. If a large length value is supplied within a certain chunk of a DVR-MS file, a heap allocation for the chunk data can fail and the return value of the allocation routine will not be checked for an error. A pointer value is calculated using the return value and the supplied length value. This condition can allow an attacker to write two null bytes to an arbitrary location in memory and this may result in the execution of arbitrary code.


Exploitation of this vulnerability results in the execution of arbitrary code with the privileges of the user viewing the Web page or opening the DVR-MS file. Since Windows Media Player supported files can be embedded into Web pages, this vulnerability can be exploited as a typical browser vulnerability. To exploit this vulnerability, a targeted user must load a malicious Web page that an attacker created. An attacker typically accomplishes this via social engineering or injecting content into compromised, trusted sites. After the user visits the malicious Web page, no further user interaction is needed.


The following Microsoft products are vulnerable:

  • Windows XP Media Center Edition 2005 SP 3
  • Windows XP SP 3
  • Windows XP Professional x64 Edition SP 2
  • Windows Vista SP 2
  • Windows Vista x64 Edition SP 2
  • Windows 7 for 32-bit Systems and Windows 7 for 32-bit Systems SP 1
  • Windows 7 for x64-based Systems and Windows 7 for x64-based Systems SP 1
  • 7 for 32-bit Systems SP 1
  • Windows 7 for x64-based Systems and Windows 7 for x64-based Systems SP 1


It is possible to use Windows ACLs to block access to the vulnerable library. To prevent this library from loading, use the calcs program included with Windows:

cacls "%windir%system32encdec.dll" /E /P everyone:N

This will prevent Windows Media Player from loading this library. To undo this workaround, use the following command:

cacls "%windir%system32encdec.dll" /E /Reveryone


Microsoft has released updates to address this vulnerability. For more information, consult their advisory at the following URL.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2011-3401 to this issue. This is a candidate for inclusion in the CVE list (, which standardizes names for security problems.


08/24/2011 Initial Vendor Notification
08/24/2011 Initial Vendor Reply
12/13/2011 Coordinated Public Disclosure


The discoverer of this vulnerability wishes to remain anonymous.

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Copyright © 2011 Verisign, Inc.

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