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CERT^® Advisory CA-2001-28 Automatic Execution of Macros

Original release date: October 08, 2001
Last revised: Mon Oct 15 09:32:36 EDT 2001
Source: CERT/CC

A complete revision history can be found at the end of this file.

Systems Affected

Systems running:

Windows
- Microsoft Excel 2000
- Microsoft Excel 2002
- Microsoft PowerPoint 2000
- Microsoft PowerPoint 2002
Macintosh
- Microsoft Excel 98
- Microsoft Excel 2001
- Microsoft PowerPoint 98
- Microsoft PowerPoint 2001

According to Microsoft, versions of Excel and PowerPoint (or indeed, other products in the Office suite) prior to this may be affected, but may be outside of hotfix support. [For example, Symantec states that Microsoft Excel 97 and Microsoft Powerpoint 97 are vulnerable.] Because Microsoft Excel 97 and Microsoft Powerpoint 97 are outside of the hotfix support window, these products may be vulnerable, but not eligible for a hotfix. For more information regarding hotfix eligibility status, please see the Microsoft Product Support Services webpage. In general, Microsoft no longer tests software outside of hotfix status for vulnerabilities, and does not provide patches to address vulnerabilities that may be discovered in that software.

Quoting from Microsoft Security Bulletin MS01-050

It's important to understand that Excel and PowerPoint 97 do not have the same macro security framework as Excel and PowerPoint 2000 and 2002. The Excel and PowerPoint 97 macro security framework lacks many key features that the 2000 and 2002 macro security framework has, including a digital signature trust model that allows trusted, signed macros to be differentiated from untrusted, unsigned macros. Under this older framework, it is difficult for a user to make an informed decision regarding the trustworthiness of macros. In addition, as noted under "Tested Versions", Excel and PowerPoint 97 are no longer supported products. Because of these two issues, customers who are concerned about macro security are urged to upgrade to a support version with a more robust macro security model.

Overview

An intruder can include a specially crafted macro in a Microsoft Excel or PowerPoint document that can avoid detection and run automatically regardless of the security settings specified by the user.

I. Description

Microsoft Excel and PowerPoint scan documents when they are opened and check for the existence of macros. If the document contains macros, the user running Excel or PowerPoint is alerted and asked if he would like the macros to be run. However, Microsoft Excel and PowerPoint may not detect malformed macros, so a user can unknowingly run macros containing malicious code when opening an Excel or PowerPoint document.

An intruder who can entice or deceive a victim into opening a document using a vulnerable version of Excel or PowerPoint could take any action the victim could take, including, but not limited to

reading, deleting, or modifying data, either locally or on open file shares
modifying security settings (including macro virus protection settings)
sending electronic mail
posting data to or retrieving data from web sites

For more information, please see

http://securityresponse.symantec.com/avcenter/security/Content/2001.10.04.html

http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS01-050.asp

Given the strong potential for widespread abuse of this vulnerability, we strongly recommend that you apply patches as soon as you are able. For example, the Melissa virus which spread in March of 1999 used social engineering to convince victims to execute a macro embedded in a Microsoft Word document. For more information, see the CERT/CC Advisory listed below.

http://www.cert.org/advisories/CA-1999-04.html

As a general practice, everyone should be aware of the potential damage that Trojan horses and other kinds of malicious code can cause to any platform. For more information, see

http://www.cert.org/advisories/CA-1999-02.html

This vulnerability has been assigned the identifier CAN-2001-0718 by the Common Vulnerabilities and Exposures (CVE) group:

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2001-0718

II. Impact

An attacker can execute arbitrary code on the target system with the privileges of the victim running Excel or PowerPoint.

III. Solution

Apply a patch

Appendix A contains information from vendors who have provided information for this advisory. We will update the appendix as we receive more information. If a vendor's name does not appear, then the CERT/CC did not hear from that vendor. Please contact your vendor directly.

Until a patch can be applied, and as a general practice, we recommend using caution when opening attachments. However, it is important to note that relying on the "From" line in an electronic mail message is not sufficient to authenticate the origin of the document.

Appendix A. - Vendor Information

This appendix contains information provided by vendors for this advisory. When vendors report new information to the CERT/CC, we update this section and note the changes in our revision history. If a particular vendor is not listed below, we have not received their comments.

Microsoft Corporation

See Microsoft Security Bulletin MS01-050

Appendix B. - References

The CERT Coordination Center thanks Peter Ferrie and Symantec Security Response, who discovered this vulnerability and published the information in their advisory. Additionally, we thank Microsoft Corporation, who published an advisory on this issue.

Author: Ian A. Finlay and Shawn V. Hernan.

This document is available from: http://www.cert.org/advisories/CA-2001-28.html

CERT/CC Contact Information

Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:

CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.

CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends.

Using encryption

We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from

http://www.cert.org/CERT_PGP.key

If you prefer to use DES, please call the CERT hotline for more information.

Getting security information

CERT publications and other security information are available from our web site

http://www.cert.org/

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Revision History

October 8, 2001:  initial release
October 11,2001:  added information to systems affected section
October 15,2001:  revised systems affected section

CERT® Advisory CA-2001-28 Automatic Execution of Macros