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Microsoft Excel FNGROUPNAME Record Uninitialized Memory Vulnerability



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


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.


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.


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.


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.


Microsoft Corp. has released a patch which addresses this issue. Information about downloadable vendor updates can be found by clicking on the URLs shown.


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 (, which standardizes names for security problems.


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


This vulnerability was discovered by Sean Larsson, iDefense Labs.

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Copyright © 2010 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.