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             AUSCERT External Security Bulletin Redistribution

                 ESB-2001.544 -- CERT Advisory CA-2001-36
   Microsoft Internet Explorer Does Not Respect Content-Disposition and
                        Content-Type MIME Headers
                             20 December 2001

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:                Internet Explorer 6.0 HTML Rendering Engine
                        Internet Explorer 6.0
                        Outlook
                        Outlook Express
Vendor:                 Microsoft
Operating System:       Windows
Impact:                 Execute Arbitrary Code/Commands
Access Required:        Remote

Ref:                    ESB-2001.534

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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

Overview

   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
   system.

   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

     http://www.microsoft.com/technet/security/bulletin/MS01-058.asp

   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:
   
   		http://www.microsoft.com/technet/security/bulletin/MS01-058.asp
   
   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
   comments.

   Microsoft Corporation

      The following documents regarding this vulnerability are available
      from Microsoft:
      
      	http://www.microsoft.com/technet/security/bulletin/MS01-058.asp
      	http://support.microsoft.com/default.aspx?scid=kb;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:
   http://www.cert.org/advisories/CA-2001-36.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
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   http://www.cert.org/

   To subscribe to the CERT mailing list for advisories and bulletins,
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   * "CERT" and "CERT Coordination Center" are registered in the U.S.
   Patent and Trademark Office.
   ______________________________________________________________________

   NO WARRANTY
   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

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