Public Vulnerability Reports

Microsoft Excel Malformed Object Memory Corruption Vulnerability

12.09.08

BACKGROUND

Excel is the spreadsheet application included with Microsoft Corp.'s Office productivity software suite. More information is available at the following website:

http://office.microsoft.com/excel/

DESCRIPTION

Remote exploitation of a memory corruption vulnerability in Microsoft Corp.'s Excel spreadsheet could allow attackers to execute arbitrary code with the privileges of the current user.

This issue exists in the handling of certain malformed object records within an Excel spreadsheet (XLS), allowing memory corruption to occur. This could lead to an exploitable situation.

iDefense's proof of concept code can redirect the program execution flow to a user controllable address on Excel 2000 SP3, and crash on other versions of Excel, including Excel XP SP3, Excel 2003 SP3 and Excel 2007 SP1.

ANALYSIS

Exploitation allows an attacker to execute arbitrary code in the context of the currently logged-on user. To exploit this vulnerability, the attacker must persuade a user to open a specially crafted Excel (XLS) document.

Likely attack vectors include sending the file as an e-mail attachment or linking to the file on a website. By default, systems with Office 2000 installed will open Office documents, including Excel spreadsheet files, from websites without prompting the user. This allows attackers to exploit this vulnerability without user interaction. Later versions of Office do not open these documents automatically unless the user has chosen this behavior.

Using the Office Document Open Confirmation Tool for Office 2000 can prevent Office files from opening automatically from web sites. Use of this tool is highly recommended for users still using Office 2000.

DETECTION

iDefense has confirmed the existence of this vulnerability with Office 2000 SP3 fully patched as of July 2008.

WORKAROUND

iDefense is currently unaware of any effective workaround for this issue, since the vulnerability exists in the core component of Excel.

VENDOR RESPONSE

Microsoft Corp. has released a patch which addresses this issue. For more information, consult their advisory at the following URL.

http://www.microsoft.com/technet/security/bulletin/ms08-074.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-4265 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

07/21/2008 Initial Vendor Notification
07/22/2008 Initial Vendor Reply
07/24/2008 Additional Vendor Feedback
12/09/2008 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.