iDefense Security Advisory 08.12.08
http://labs.idefense.com/intelligence/vulnerabilities/
Aug 12, 2008

I. BACKGROUND

Microsoft Excel is the spreadsheet application that is 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 invalid array indexing vulnerability in
Microsoft Corp.'s Excel could allow an attacker to execute arbitrary
code with the privileges of the current user.

This issue exists in the handling of "AxesSet" records within a chart
embedded in a spreadsheet. This record is typically used for setting
the location and size of a set of axes on a chart. This particular
record type is not included in Microsoft's official documentation for
the Excel file format. However, the freely available source code for
OpenOffice implements this record type.

When processing this record, Excel does not validate a value that is
used as an index into the array of chart axes. By crafting an Excel
spreadsheet (XLS) that contains an out-of-bounds array value, an
attacker can cause memory corruption. This leads to a potentially
exploitable condition.

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 on web sites from opening automatically. 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 SP-3 fully patched as of March 2008. Other versions may also be
affected.

V. WORKAROUND

iDefense is currently unaware of any effective workaround for this
issue.

VI. VENDOR RESPONSE

Microsoft has officially addressed this vulnerability with Security
Bulletin MS08-043. For more information, consult their bulletin at the
following URL.

http://www.microsoft.com/technet/security/bulletin/ms08-043.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2008-3004 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

03/27/2008  Initial vendor notification
03/31/2008  Initial vendor response
08/12/2008  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2008 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.