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Home » Hacking News » CERT - CA-2001-36 - Internet Explorer

CERT - CA-2001-36 - Internet Explorer

by Nikola Strahija on December 21st, 2001 Microsoft Internet Explorer contains a vulnerability in its handling of certain MIME headers in web pages and HTML email messages. This vulnerability may allow an attacker to execute arbitrary code on the victim's system when the victim visits a web page or views an HTML email message.


CERT Advisory CA-2001-36 Microsoft Internet Explorer Does Not Respect
Content-Disposition and Content-Type MIME Headers

Original release date: December 19, 2001
Last revised: --
Source: CERT/CC

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

Systems Affected

* Microsoft Internet Explorer 6.0 for Windows
* Microsoft Outlook, Outlook Express, or any other software that
utilizes vulnerable versions of Internet Explorer to render HTML


Microsoft Internet Explorer contains a vulnerability in its handling of
certain MIME headers in web pages and HTML email messages. This
vulnerability may allow an attacker to execute arbitrary code on the
victim's system when the victim visits a web page or views an HTML
email message.

I. Description

Web pages and HTML email messages usually contain HTML text, but other
files may also be included. The MIME headers Content-Disposition and
Content-Type provide the information needed by the HTML rendering
software to determine the type of these files. In Microsoft Internet
Explorer, these MIME headers are consulted when evaluating whether to
process an embedded file, but they are ignored when the file is
actually processed.

For example, if an executable (.exe) file is embedded with MIME headers
that misrepresent it as a JPEG image file (.jpg), Internet Explorer
will treat the file as a JPEG when evaluating whether it is safe to
open. Once this evaluation is complete, the file will be opened
according to its .exe file extension and will be executed on the local

This behavior results in a vulnerability that allows attackers to
bypass the security measures that typically screen out executable code.
This code would be executed with the privileges the user who views the
web page or email message.

Users who view a malicious web site or HTML email message may be able
to prevent the execution of the attacker's code by using the download
progress dialog box to cancel the download. However, depending on the
size of the embedded file and the speed of the network connection,
users may not have time to cancel the file download.

The CERT/CC is tracking this vulnerability as VU#443699, which
corresponds directly to the "File Execution" vulnerability described in
Microsoft Security Bulletin MS01-058. This Microsoft bulletin is
available at

This vulnerability is being referenced in CVE as CAN-2001-0727.

II. Impact

By convincing a user to view a malicious web page or HTML email
message, a remote attacker can cause the user to execute arbitrary
code. Any such code would run with the privileges of the user who
attempted to view the content.

III. Solution

Apply a patch from your vendor

Microsoft has released a cumulative patch for Internet Explorer that
corrects this vulnerability and several others. For more information
about the patch and the vulnerabilities, please see Microsoft
Security Bulletin MS01-058:

Disable file downloads in all security zones

As a workaround, you can prevent malicious files from being
downloaded by disabling file downloads in all security zones. Note
that this decision will impact browser functionality.

Appendix A. - Vendor Information

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

Microsoft Corporation

The following documents regarding this vulnerability are available
from Microsoft:;EN-US;q313675

The CERT Coordination Center acknowledges Jouko Pynnonen as the
discoverer of this vulnerability and thanks Microsoft for the
information presented in MS01-058.

Author: This document was written by Jeffrey P. Lanza.

This document is available from:

CERT/CC Contact Information

Email: [email protected]
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

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

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

Getting security information

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

To subscribe to the CERT mailing list for advisories and bulletins,
send email to [email protected] Please include in the body of your

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* "CERT" and "CERT Coordination Center" are registered in the U.S.
Patent and Trademark Office.

Any material furnished by Carnegie Mellon University and the Software
Engineering Institute is furnished on an "as is" basis. Carnegie Mellon
University makes no warranties of any kind, either expressed or implied
as to any matter including, but not limited to, warranty of fitness for
a particular purpose or merchantability, exclusivity or results
obtained from use of the material. Carnegie Mellon University does not
make any warranty of any kind with respect to freedom from patent,
trademark, or copyright infringement.

Conditions for use, disclaimers, and sponsorship information

Copyright 2001 Carnegie Mellon University.

Revision History

December 19, 2001: Initial release

Version: PGP 6.5.8


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