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iDefense Security Advisory 11.10.09
http://labs.idefense.com/intelligence/vulnerabilities/
Nov 10, 2009

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 memory corruption vulnerability in Microsoft
Corp.'s Excel could allow an attacker to execute arbitrary code with
the privileges of the current user.

The vulnerability occurs when parsing a FEATHEADER record within an
Excel file. This record is used to store information common to multiple
other records, and was introduced with Excel 2002 (XP). When certain
fields of this record are set to a trigger value, it is possible to
corrupt memory in such a way that the next 4 bytes in the record are
treated as an object pointer. This pointer is then used to make a
virtual function call, which results in the execution of arbitrary
code.

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.

Labs testing has demonstrated this vulnerability is highly exploitable.
However, on systems where they are present, anti-exploitation
technologies like DEP and ASLR make the vulnerability extremely
difficult to exploit in a reliable way.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Excel
versions 2007, 2003, and XP. The record that causes the vulnerability
is not supported by Excel 2000, so it is not affected by this
vulnerability.

V. WORKAROUND

The vulnerability occurs in the core parsing code of Excel, and this
code can not be disabled. However, it is possible to disable the
opening of the older binary format files, and use MOICE to convert the
file to the newer XML based format. These two methods are linked to in
the Sources section.

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/MS09-067.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2009-3129 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

04/30/2009  - Initial Contact
04/30/2009  - Initial Vendor Response
11/10/2009  - Coordinated Public Disclosure

IX. CREDIT

This vulnerability was discovered by Sean Larsson, iDefense Labs.

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php

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http://labs.idefense.com/

X. LEGAL NOTICES

Copyright © 2009 iDefense, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDefense. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically,
please e-mail customerservice@idefense.com for permission.

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.
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