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Microsoft Excel Chart AxesSet Invalid Array Index Vulnerability

08.12.08

BACKGROUND

Microsoft Excel is the spreadsheet application that is 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 an invalid array indexing vulnerability in Microsoft Corp.'s Excel could allow an attacker to execute arbitrary code with the privileges of the current user.

This issue exists in the handling of "AxesSet" records within a chart embedded in a spreadsheet. This record is typically used for setting the location and size of a set of axes on a chart. This particular record type is not included in Microsoft's official documentation for the Excel file format. However, the freely available source code for OpenOffice implements this record type.

When processing this record, Excel does not validate a value that is used as an index into the array of chart axes. By crafting an Excel spreadsheet (XLS) that contains an out-of-bounds array value, an attacker can cause memory corruption. This leads to a potentially exploitable condition.

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 on web sites from opening automatically. 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 SP-3 fully patched as of March 2008. Other versions may also be affected.

WORKAROUND

iDefense is currently unaware of any effective workaround for this issue.

VENDOR RESPONSE

Microsoft has officially addressed this vulnerability with Security Bulletin MS08-043. For more information, consult their bulletin at the following URL.

http://www.microsoft.com/technet/security/bulletin/ms08-043.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-3004 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

03/27/2008 Initial vendor notification
03/31/2008 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.