iDefense Security Advisory 12.11.07: Microsoft DirectX 7 and 8 DirectShow Stack Buffer Overflow Vulnerability

Type securityvulns
Reporter Securityvulns
Modified 2007-12-13T00:00:00


iDefense Security Advisory 12.11.07 Dec 11, 2007


Microsoft DirectShow, part of Microsoft DirectX, is used for the capture and playback of multimedia streams on Microsoft Windows systems. Synchronized Accessible Media Interchange (SAMI) is a file format designed by Microsoft Corp. to deliver captions, subtitles, or audio descriptions synchronized with digital media content.


Remote exploitation of a stack buffer overflow vulnerability in Microsoft Corp.'s DirectShow could allow an attacker to execute arbitrary code in the context of the current user.

This vulnerability exists in the DirextShow SAMI parser, which is implemented in quartz.dll. When the SAMI parser copies parameters into a stack buffer, it does not properly check the length of the parameter. As such, parsing a specially crafted SAMI file can cause a stack-based buffer overflow. This allows an attacker to execute arbitrary code.


Exploitation allows an attacker to execute arbitrary code in the context of the current user.

In order to exploit this vulnerability, an attacker must persuade a user to open a malicious SAMI file. This can be accomplished by hosting a malicious SAMI file on a web site or by sending the malicious file to a user via e-mail or instant message.

It is important to note that a SAMI file does not necessarily have to end with a .smi or .sami extension. DirectShow will identify the file based on the file contents.

If "Web View Content" is enabled in Windows Explorer, which is the default setting, a single click will open the malicious file in the preview pane and trigger the vulnerability.

DirectX 9.0c is listed as an optional update for Windows 2000 operating system in Windows Update site. It is not listed as a critical update. However, installing this update will remove this vulnerability.


iDefense has confirmed Microsoft DirectX 7.x and Microsoft DirectX 8.x are vulnerable. Microsoft DirectX 9.0c or newer is not vulnerable.


To prevent exploitation of this vulnerability, upgrade to DirectX 9.0c or newer.

If upgrading is not possible, you can prevent access to the vulnerable code by un-registering quartz.dll as shown below. However, this workaround will disable image, audio, and video rendering in DirectX-enabled applications.

C:\> regsvr32 -u %windir%\system32\quartz.dll


Microsoft has addressed this vulnerability within Microsoft Security Bulletin MS07-064. For more information, consult their bulletin at the following URL.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2007-3901 to this issue. This is a candidate for inclusion in the CVE list (, which standardizes names for security problems.


09/28/2007 Initial vendor notification 10/09/2007 Initial vendor response 12/11/2007 Coordinated public disclosure


This vulnerability was discovered by Jun Mao of VeriSign iDefense Labs.

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Copyright © 2007 iDefense, Inc.

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