US-CERT Technical Cyber Security Alert TA06-167A -- Microsoft Excel Vulnerability

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National Cyber Alert System

Technical Cyber Security Alert TA06-167A

Microsoft Excel Vulnerability

Original release date: June 16, 2006
Last revised: --
Source: US-CERT

Systems Affected

* Microsoft Excel 2003
* Microsoft Excel XP (2002)
* Microsoft Excel for Mac

Microsoft Excel is included with Microsoft Office. Other versions of
Excel, and other Office programs may be affected or act as attack


An unspecified vulnerability in Microsoft Excel could allow an
attacker to execute arbitrary code on a vulnerable system.

I. Description

Microsoft Excel contains an unspecified vulnerability. Opening a
specially crafted Excel document, including documents hosted on web
sites or attached to email messages, could trigger the vulnerability.

Office documents can contain embedded objects. For example, a
malicious Excel document could be embedded in an Word or PowerPoint
document. Office documents other than Excel documents could be used as
attack vectors.

For more information, please see Vulnerability Note VU#802324.

II. Impact

By convincing a user to open a specially crafted Excel document, an
attacker could execute arbitrary code on a vulnerable system. If the
user has administrative privileges, the attacker could gain complete
control of the system.

III. Solution

At the time of writing, there is no complete solution available.
Consider the following workarounds:

Do not open untrusted Excel documents

Do not open unfamiliar or unexpected Excel or other Office documents,
including those received as email attachments or hosted on a web site.
Please see Cyber Security Tip ST04-010 for more information.

Do not rely on file extension filtering

In most cases, Windows will call Excel to open a document even if the
document has an unknown file extension. For example, if document.x1s
(note the digit "1") contains the correct file header information,
Windows will open document.x1s with Excel.

Appendix A. References

* Vulnerability Note VU#802324 -

* Cyber Security Tip ST04-010 -


Information used in this document came from SANS and Microsoft.

The most recent version of this document can be found at:


Feedback can be directed to US-CERT Technical Staff. Please send
email to <cert@xxxxxxxx> with "TA06-167A Feedback VU#802324" in the

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Produced 2006 by US-CERT, a government organization.

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Revision History

June 16, 2006: Initial release

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