Microsoft Excel Filter Record Code Execution Vulnerability

iDefense Security Advisory 05.08.07
http://labs.idefense.com/intelligence/vulnerabilities/
May 08, 2007

I. BACKGROUND

Microsoft Excel is the spreadsheet application from the Microsoft Office
System. More information is available at the following URL.

http://office.microsoft.com/

II. DESCRIPTION

Remote exploitation of an input validation error in the handling of
AutoFilter records in Excel BIFF8 format spreadsheet files by Microsoft
Corp.'s Excel 2003 could allow an attacker to execute arbitrary code in
the context of the current user.

The AutoFilter feature of Excel allows data not matching a specified
criteria to be filtered out. By creating a document containing a
specially crafted filter record, an attacker is able to cause an
invalid memory access leading to arbitrary code execution.

III. ANALYSIS

Exploitation allows attackers to execute arbitrary code in the context
of the user who started Excel.

Exploitation requires that attackers social engineer users into opening
a maliciously crafted file in Excel. Reliable exploitation appears to
require knowledge of the specific version of Excel being used. 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 open Office documents,
including Excel spreadsheet files, from websites without prompting the
user, which 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.

Enabling hardware DEP (data execution prevention) on systems that
support it (i.e., Windows XP SP2 and Windows Server 2003 on hardware
with AMD processors that support NX or Intel processors supporting XD)
mitigates this vulnerability. The hardware DEP feature prevents code
from being executed from areas of memory that do not have the
'executable' bit set. While it may be possible for attackers to bypass
this restriction, it can prevent some typical exploitation methods.

IV. DETECTION

iDefense has confirmed Microsoft Excel 2003 is vulnerable. Previous
versions are also likely to be affected. Excel 2007 does not appear to
be vulnerable.

V. WORKAROUND

iDefense is currently unaware of an effective workarounds for this
issue.

VI. VENDOR RESPONSE

Microsoft has addressed this vulnerability within MS07-023. For more
information, consult their bulletin at the following URL.

http://www.microsoft.com/technet/security/Bulletin/MS07-023.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-1214 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

02/08/2007  Initial vendor notification
02/08/2007  Initial vendor response
05/08/2007  Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Greg MacManus (iDefense Labs).

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X. LEGAL NOTICES

Copyright © 2007 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
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