TUCoPS :: Browsers :: ca200106.txt

MSIE: Automatic Execution of Embedded MIME Types

From cert-advisory@cert.org Wed Apr  4 10:14:51 2001
Date: Tue, 3 Apr 2001 14:02:33 -0400 (EDT)
From: CERT Advisory <cert-advisory@cert.org>
To: cert-advisory@cert.org
Subject: CERT Advisory CA-2001-06


CERT Advisory CA-2001-06 Automatic Execution of Embedded MIME Types

   Original release date: April 03, 2001
   Last revised: --
   Source: CERT/CC

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

Systems Affected

     * All versions of Microsoft Internet Explorer 5.5 SP1 or earlier,
       except IE 5.01 SP2
     * Any software which utilizes vulnerable versions of Internet
       Explorer to render HTML


   Microsoft Internet Explorer has a vulnerability triggered when parsing
   MIME parts in a document that allows a malicious agent to execute
   arbitrary code. Any user or program that uses vulnerable versions of
   Internet Explorer to render HTML in a document (for example, when
   browsing a filesystem, reading email or news messages, or visiting a
   web page), should immediately upgrade to a non-vulnerable version of
   Internet Explorer.

I. Description

   There exists in Internet Explorer a table which is used to determine
   how IE handles MIME types when it encounters MIME parts in any type of
   HTML document, be it email message, newsgroup posting, web page, or
   local file. This table contains a set of entries that cause Internet
   Explorer to open the MIME part without giving the end user the
   opportunity to decide if the MIME part should be opened. This
   vulnerability allows an intruder to construct malicious content that,
   when viewed in Internet Explorer (or any program that uses the IE HTML
   rendering engine), can execute arbitrary code. It is not necessary to
   run an attachment; simply viewing the document in a vulnerable program
   is sufficient to execute arbitrary code.

   For more details, see Microsoft Security Bulletin MS01-020 on this
   topic at:


   There have been reports that simply previewing HTML content (as in a
   mail client or filesystem browser) is sufficient to trigger the
   vulnerability. The impact of viewing malicious code in this manner is
   being evaluated.

   The CERT/CC is currently unaware of any reports of this vulnerability
   being used to successfully attack a system. Demonstration code
   exploiting this vulnerability has been published in several public
   forums. This vulnerability is being referenced in CVE as CAN-2001-0154
   and by the CERT/CC as VU#980499.

II. Impact

   Attackers can cause arbitrary code to be executed on a victim's system
   by embedding the code in a malicious email, or news message, or web

III. Solution

Apply the patch from Microsoft

   Apply the patch from Microsoft, available at:


   As noted in the 'Caveats' section of the Microsoft advisory, end users
   must apply this patch to supported versions of Microsoft's browser.
   This means IE must be upgraded to IE 5.01 Service Pack 1 or IE 5.5
   Service Pack 1 before users can apply this patch. Users who have not
   previously upgraded will incorrectly receive a message stating that
   they do not need to apply this patch, even though they are vulnerable.
   Users are advised to upgrade to IE 5.5 SP1, IE 5.01 SP1 or SP2 (which
   has this patch incorporated in it) and apply the appropriate patch.

   An excerpt from MS01-020:

 If the patch is installed on a system running a version of IE other
 than the one it is designed for, an error message will be displayed
 saying that the patch is not needed. This message is incorrect, and
 customers who see this message should upgrade to a supported version
 of IE and re-install the patches.

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

Cyrusoft International, Inc.

   Mulberry does not use Internet Explorer to render HTML within Mulberry
   itself and is not vulnerable to these kinds of problems. Users can
   save HTML attachments to disk and then view those in browsers
   susceptible to this problem, but this requires the direct intervention
   of the user to explicitly save to disk - simply viewing HTML in
   Mulberry does not expose users to these kinds of problems.

   Our HTML rendering is a basic styled-text only renderer that does not
   execute any form of scripts. This is true on all the platforms we
   support: Win32, Mac OS (Classic & X), Solaris, linux.

   An official statement about this is available on our website at:


Lotus Development Corporation

   Notes does not use IE to render HTML-formatted mail messages.

Microsoft Corporation

   Please see the advisory (MS01-020, "Incorrect MIME Header Can Cause IE
   to Execute E-mail Attachment") related to this issue at:


   A patch is available for this issue at:


Netscape Communications Corporation

   Netscape is currently investigating the impact this vulnerability, if
   any, has on users of the Netscape browser.

Opera Software

   Opera does not use Internet Explorer or any other external software to
   render HTML.

QUALCOMM Incorporated

   It is unclear at this time what impact, if any, this vulnerability has
   on Eudora clients.

Appendix B. - References

    1. Havrilla, J., and Hernan, S., "CERT Vulnerability Note VU#980499:
       Certain MIME types can cause Internet Explorer to execute
       arbitrary code when rendering HTML", March 2001.

   Microsoft has acknowledged Juan Carlos Cuartango for bringing this
   issue to their attention.

   This document was written by Jeffrey S. Havrilla and Shawn V. Hernan.
   If you have feedback, comments, or additional information about this
   issue, please send us email.
   This document is available from:

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

   CERT personnel answer the hotline 08:00-20:00 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 majordomo@cert.org. Please include in the body of your

   subscribe cert-advisory

   * "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
April 03, 2001:  Initial release

Version: PGP for Personal Privacy 5.0
Charset: noconv


TUCoPS is optimized to look best in Firefox® on a widescreen monitor (1440x900 or better).
Site design & layout copyright © 1986-2024 AOH