iDefense Security Advisory 12.11.07
http://labs.idefense.com/intelligence/vulnerabilities/
Dec 11, 2007

I. BACKGROUND

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.

http://msdn2.microsoft.com/en-us/library/ms783323.aspx

http://msdn2.microsoft.com/en-us/library/bb248347.aspx

II. DESCRIPTION

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.

III. ANALYSIS

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.

IV. DETECTION

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

V. WORKAROUND

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

VI. VENDOR RESPONSE

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

http://www.microsoft.com/technet/security/Bulletin/MS07-064.mspx

VII. CVE INFORMATION

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 (http://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

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

IX. CREDIT

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

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
 There are no warranties with regard to this information. Neither the
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