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

This vulnerability is a type confusion vulnerability that occurs when
parsing several related Excel record types. In this case, the type
confusion is due to multiple records containing fields that identify
the type of an object shared between them.

By controlling memory outside of the bounds of the allocated heap chunk,
an attacker can control a C++ object pointer used in a virtual function
call. This can result in an area of memory being treated as a different
type of object than it actually is, resulting in access outside of the
bounds of the allocated object.

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. This is typically accomplished by emailing the targeted user a
malicious file, or providing a link to one on a webpage.

iDefense testing has demonstrated that this vulnerability is highly
exploitable, which is consistent with most type confusion
vulnerabilities.

As with most memory corruption vulnerabilities, exploitation mitigation
technologies like DEP and ASLR substantially increase the difficulty of
exploiting this vulnerability.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in all
currently supported versions of Excel (2007 SP1/SP2, 2003 SP3, XP SP3),
and also the currently unsupported Excel 2000 SP3. 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 it is impossible to
disable the affected module.

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-2010-0258 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

09/10/2009  Initial Vendor Notification
09/11/2009  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.