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Microsoft Office BMP Input Filter Heap Overflow Vulnerability

08.12.08

BACKGROUND

Microsoft Office contains a number of input filters. These input filters allow transparent conversion from external types into a form that the Office applications can use. More information on import filters in Microsoft Office 2002 is available at the following URL.

http://support.microsoft.com/?scid=kb;en-us;290362

DESCRIPTION

Remote exploitation of a heap buffer overflow vulnerability in the "BMPIMP32.FLT" filter module, as distributed with Microsoft Office, allows attackers to execute arbitrary code.

The vulnerability specifically exists in the handling of Windows Bitmap (BMP) image files with malformed headers. By specifying a very large number of colors in the header, it is possible to cause controllable heap corruption, which can be leveraged to execute arbitrary code.

ANALYSIS

Exploitation could allow attackers to execute arbitrary code on the targeted host under the security context of the current logged in user. Successful exploitation would require the attacker to entice his or her victim into opening a specially crafted BMP image with a vulnerable version of Office.

DETECTION

iDefense confirmed that the "BMPIMP32.FLT" module installed with Microsoft Office XP SP3, including all patches as of May 24, 2006, is vulnerable. Other versions may also be vulnerable.

This vulnerability does not affect Microsoft Office 2003 as this filter is not installed or required.

WORKAROUND

This workaround replaces the affected filter with an empty file. Creating this file prevents Office from offering to reinstall the affected component.

 1. Close all running applications. 2. Open the folder "C:Program FilesCommon FilesMicrosoft SharedGrphflt". 3. Rename the file "BMPIMP32.FLT" to "BMPIMP.FLT.disabled". 4. Create an empty file in this directory with the name "BMPIMP32.FLT". (Open Notepad, go to this directory and choose File, Save..., type "BMPIMP32.FLT" including the quotes and click Save. 

In testing on Windows 2000 with Office XP SP3 installed, this workaround did not adversely impact functionality. BMP format image files can still be imported into Word, but the operations that can be performed on them may be impacted.

VENDOR RESPONSE

Microsoft has officially addressed this vulnerability with Security Bulletin MS08-044. For more information, consult their bulletin at the following URL.

http://www.microsoft.com/technet/security/bulletin/ms08-044.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-3020 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.

DISCLOSURE TIMELINE

09/11/2006 Initial vendor notification
09/11/2006 Initial vendor response
08/12/2008 Coordinated public disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2008 Verisign, 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 author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.