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iDefense Security Advisory 12.09.08
http://labs.idefense.com/intelligence/vulnerabilities/
Dec 09, 2008

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 spreadsheet could allow attackers to execute arbitrary
code with the privileges of the current user.

This issue exists in the handling of certain malformed object records
within an Excel spreadsheet (XLS), allowing memory corruption to occur.
This could lead to an exploitable situation.

iDefense's proof of concept code can redirect the program execution flow
to a user controllable address on Excel 2000 SP3, and crash on other
versions of Excel, including Excel XP SP3, Excel 2003 SP3 and Excel
2007 SP1.

III. 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 from opening automatically from web sites. Use of
this tool is highly recommended for users still using Office 2000.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability with Office
2000 SP3 fully patched as of July 2008.

V. WORKAROUND

iDefense is currently unaware of any effective workaround for this
issue, since the vulnerability exists in the core component of Excel.

VI. VENDOR RESPONSE

Microsoft Corp. has released a patch which addresses this issue. For
more information, consult their advisory at the following URL.

http://www.microsoft.com/technet/security/bulletin/ms08-074.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-4265 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

07/21/2008  Initial Vendor Notification
07/22/2008  Initial Vendor Reply
07/24/2008  Additional Vendor Feedback
12/09/2008  Coordinated Public Disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
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X. LEGAL NOTICES

Copyright © 2008 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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