Microsoft Excel Long Palette Heap Overflow Vulnerability

iDefense Security Advisory 01.09.07
http://labs.idefense.com/intelligence/vulnerabilities/ 
Jan 09, 2007

I. BACKGROUND

Microsoft Excel is the spreadsheet application from the Microsoft Office
System. More information is available at the following link:

http://office.microsoft.com/ 

II. DESCRIPTION

Remote exploitation of an heap-based buffer overflow vulnerability in
Microsoft Corp.'s Excel spreadsheet application format could allow an
attacker to execute arbitrary code in the context of the user who started
Excel.

The vulnerability specifically exists in the handling of the PALETTE
record in BIFF8 format spreadsheet files. By supplying a record with too
many entries, an exploitable buffer overflow condition can occur.

III. ANALYSIS

Successful exploitation of this vulnerability would allow an attacker to
execute arbitrary code in the context of the user who opened the document.
In order exploit this vulnerability, an attacker would need to convince the
target to open an Excel spreadsheet file. Likely attack vectors include
sending the file as an attachment in an email or linking to the file on a
website.

Systems with a default install of Office 2000 will open Office documents,
including Excel spreadsheet files, from websites without prompting the
user. This allows an attacker to exploit this vulnerability without user
interaction beyond visiting a website. Later versions of Office will not
open these documents automatically unless the user has chosen this
behavior.

IV. DETECTION

iDefense Labs have confirmed the existence of this vulnerability in
Microsoft Excel 2003 with all service packs and security updates. Previous
versions of Excel are also likely to be affected.

V. WORKAROUND

Do not follow links or open files from unknown sources or that you were not
expecting to receive.

VI. VENDOR RESPONSE

Microsoft has addressed this vulnerability with Microsoft Security Bulletin
MS07-002. A link to this bulletin can be found below.

http://www.microsoft.com/technet/security/bulletin/ms07-002.mspx 

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-0031 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

09/25/2006  Initial vendor notification
09/22/2006  Initial vendor response
01/09/2007  Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Greg MacManus, iDefense Labs.

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X. LEGAL NOTICES

Copyright =A9 2006 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
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.