iDefense Security Advisory 03.09.10: Microsoft Excel FNGROUPNAME Record Uninitialized Memory Vulnerability

iDefense Security Advisory 03.09.10
http://labs.idefense.com/intelligence/vulnerabilities/
Mar 09, 2010

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

The vulnerability occurs due to Excel using a local function variable
without properly initializing it. This error occurs when parsing
several related records inside of an Excel worksheet. When Execl parses
certain records in a particular order, a stack variable may not be
initialized properly. If an attacker can control the area of memory
used for this variable, then it is possible to execute arbitrary code
on the targeted host.

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.

Successful exploitation of this vulnerability depends upon an attacker
being able to control the area of uninitialized memory prior to the
vulnerable code execution. Since the data stored is a constant, this
type of vulnerability can typically be difficult to exploit.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Excel
versions 2003 SP3, 2007 SP0, SP1, and SP3 . Previous versions do not
appear to be affected. A full list of vulnerable Microsoft products can
be found in Microsoft Security Bulletin MS10-017.

V. WORKAROUND

iDefense is currently unaware of any workarounds for this issue since
the vulnerability occurs in the core parsing code, making it impossible
to disable the affected area of code.

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-2010-0262 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.