Incorrect MIME Header Can Cause IE to Execute E-mail Attachment

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===========================================================================
             AUSCERT External Security Bulletin Redistribution

           ESB-2001.131 -- Microsoft Security Bulletin MS01-020
      Incorrect MIME Header Can Cause IE to Execute E-mail Attachment
                               30 March 2001

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

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

Product:                Microsoft Internet Explorer 5.01
                        Microsoft Internet Explorer 5.5
Vendor:                 Microsoft
Impact:                 Execute Arbitrary Code/Commands
Access Required:        Remote

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Title:      Incorrect MIME Header Can Cause IE to Execute E-mail 
            Attachment
Date:       29 March 2001
Software:   Microsoft Internet Explorer
Impact:     Run code of attacker's choice.
Bulletin:   MS01-020

Microsoft encourages customers to review the Security Bulletin 
at: http://www.microsoft.com/technet/security/bulletin/MS01-020.asp.
- - ----------------------------------------------------------------------

Issue:
======
Because HTML e-mails are simply web pages, IE can render them and
open 
binary attachments in a way that is appropriate to their MIME types. 
However, a flaw exists in the type of processing that is specified
for 
certain unusual MIME types. If an attacker created an HTML e-mail 
containing an executable attachment, then modified the MIME header 
information to specify that the attachment was one of the unusual
MIME 
types that IE handles incorrectly, IE would launch the attachment 
automatically when it rendered the e-mail. 

An attacker could use this vulnerability in either of two scenarios. 
She could host an affected HTML e-mail on a web site and try to 
persuade another user to visit it, at which point script on a web
page 
could open the mail and initiate the executable. Alternatively, she 
could send the HTML mail directly to the user. In either case, the 
executable attachment, if it ran, would be limited only by user's 
permissions on the system. 

Mitigating Factors:
====================
The vulnerability could not be exploited if File Downloads have been 
disabled in the Security Zone in which the e-mail is rendered. This
is 
not a default setting in any zone, however. 

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-020.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Juan Carlos Cuartango (http://www.kriptopolis.com) 

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THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED 
"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL 
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF 
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT 
SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY
DAMAGES 
WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL,
LOSS 
OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION
OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH
DAMAGES. 
SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR
CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY 
NOT APPLY.



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