I. 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/

II. DESCRIPTION

Remote exploitation of a heap overflow vulnerability in Microsoft Corp.'s Excel could allow an attacker to execute arbitrary code with the privileges of the current user.

This vulnerability occurs when parsing an MDXTUPLE record inside of the Excel Workbook globals stream. This record is used to store metadata for external data connections in the workbook. The vulnerability occurs when a MDXTUPLE record is broken up into several records. This could allow an attacker to trigger a heap based buffer overflow by controlling both the allocation size of a heap buffer and the number of bytes copied into this buffer.

III. ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary code with the privileges of the user opening the file. To exploit this vulnerability, an attacker needs to convince a user to open a malicious file. Attackers typically accomplish this by emailing a targeted user the file, or hosting the file on a Web page.

Exploitation of this vulnerability is relatively simple. An attacker can control the size of the buffer allocated, the size of the overflow, and the content of the overflow.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Excel versions 2007 SP0, SP1, and SP2. Previous versions do not appear to be affected as they do not support parsing the record that triggers the vulnerability. A full list of vulnerable Microsoft products can be found in Microsoft Security Bulletin MS10-017.

V. WORKAROUND

Microsoft suggested workarounds can be found in Microsoft Security Bulletin MS10-017.

VI. VENDOR RESPONSE

Microsoft Corp. has released a patch which addresses this issue. Information about downloadable vendor updates can be found by clicking on the URLs shown. http://www.microsoft.com/technet/security/bulletin/MS10-017.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2010-0260 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

09/25/2009 Initial Vendor Notification
09/25/2009 Initial Vendor Reply
03/09/2010 Coordinated Public Disclosure

IX. CREDIT

This vulnerability was discovered by Sean Larsson, iDefense Labs.

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X. LEGAL NOTICES

Copyright © 2010 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.