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TUCoPS :: Windows Net Apps :: ciacl091.txt

Microsoft Exchange Server Outlook Web Access Flaw




             __________________________________________________________

                       The U.S. Department of Energy
                     Computer Incident Advisory Center
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___
             __________________________________________________________

                             INFORMATION BULLETIN

             Microsoft Exchange Server Outlook Web Access Flaw
             [Microsoft Security Bulletin MS01-030, Version 3]

[Revision A 6/20/2001 Used Version 3]
June 20, 2001 17:00 GMT                                          Number L-091A
______________________________________________________________________________
PROBLEM:       A flaw exists in the interaction between Outlook Web Access 
               (OWA) and Internet Explorer for message attachments. An 
               attachment containing html code, including script, could 
               execute when the attachment is opened regardless of the 
               attachment type. 
PLATFORM:      Microsoft Exchange 2000 and Exchange 5.5 
DAMAGE:        The flaw could execute script contained in an attachment. An 
               attacker could construct an attachment containing malicious 
               code, which would execute if the user opened it. 
SOLUTION:      Apply the patches as described below. 
______________________________________________________________________________
VULNERABILITY  The risk is LOW: The vulnerability is only exploitable by 
ASSESSMENT:    attachments that are received through OWA. It still requires 
               the user to open an attachment. Users should know not to open 
               unexpected attachments from any source. 

______________________________________________________________________________

[******  Start Microsoft Advisory ******]
----------------------------------------------------------------------
Title:      Incorrect Attachment Handling in Exchange OWA Can 
            Execute Script
Date:       06 June 2001
Revised:    13 June 2001 (version 3.0)
Software:   Exchange 5.5, Exchange 2000
Impact:     Run code of attacker's choice on mail client
Bulletin:   MS01-030

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-030.asp.
----------------------------------------------------------------------

Reason for Revision:
====================
On June 12, 2001 Microsoft discovered that the updated Exchange 2000 
patch contained outdated files. We have corrected the error and 
provided an updated version of this patch for Exchange 2000. We 
recommend that all customers who have downloaded the Exchange 2000 
patch prior to June 12, 2001 install the updated version. 

Issue:
======
OWA is a service of Exchange Server that allows users to use a web 
browser to access their Exchange mailbox. However, a flaw exists in
the 
interaction between OWA and IE for message attachments. If an 
attachment contains HTML code including script, the script will be 
executed when the attachment is opened, regardless of the attachment 
type. Because OWA requires that scripting be enabled in the zone
where 
the OWA server is located, this script could take action against the 
user's Exchange mailbox. 

An attacker could use this flaw to construct an attachment containing
malicious script code. The attacker could then send the attachment in
a 
message to the user. If the user opened the attachment in OWA, the 
script would execute and could take action against the user's mailbox
as if it were the user, including, under certain circumstances, 
manipulation of messages or folders.

Mitigating Factors:
====================
- The vulnerability could only be exploited if the user were 
   using OWA in conjunction with IE. 
 - The vulnerability is only exploitable by attachments that 
   are received via OWA. In general, an attacker would have no 
   way to determine whether a user would open an attachment 
   using OWA rather than an Outlook client. 
 - An attacker's ability to exploit this vulnerability would 
   require that she entice the user to open an attachment from 
   an untrusted source. Best practices recommend against opening 
   any attachment from an unknown or untrusted source.

Patch Availability:
===================
- A patch is available to fix this vulnerability. Please read the 
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-030.asp
   for information on obtaining this patch.

Acknowledgment:
===============
- Joao Gouveia (tharbad@kaotik.org)
---------------------------------------------------------------------

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.

[******  End Microsoft Advisory ******]

_______________________________________________________________________________

CIAC wishes to acknowledge the contributions of Microsoft for the 
information contained in this bulletin.
_______________________________________________________________________________


CIAC, the Computer Incident Advisory Center, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.

CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
    Voice:    +1 925-422-8193 (7x24)
    FAX:      +1 925-423-8002
    STU-III:  +1 925-423-2604
    E-mail:   ciac@ciac.org

Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.

   World Wide Web:      http://www.ciac.org/
   Anonymous FTP:       ftp.ciac.org

PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins.  If you are not part of these
communities, please contact your agency's response team to report
incidents. Your agency's team will coordinate with CIAC. The Forum of
Incident Response and Security Teams (FIRST) is a world-wide
organization. A list of FIRST member organizations and their
constituencies can be obtained via WWW at http://www.first.org/.

This document was prepared as an account of work sponsored by an
agency of the United States Government. Neither the United States
Government nor the University of California nor any of their
employees, makes any warranty, express or implied, or assumes any
legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately
owned rights. Reference herein to any specific commercial products,
process, or service by trade name, trademark, manufacturer, or
otherwise, does not necessarily constitute or imply its endorsement,
recommendation or favoring by the United States Government or the
University of California. The views and opinions of authors expressed
herein do not necessarily state or reflect those of the United States
Government or the University of California, and shall not be used for
advertising or product endorsement purposes.

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