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Title: Incorrect Attachment Handling in Exchange OWA Can
            Execute Script
Released: 06 June 2001
Revised: 08 June 2001 (version 2.0)
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.
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Reason for Revision:
====================
 - Exchange 5.5 has been determined to be affected by the
   vulnerability. We have developed an Exchange 5.5 patch.
 - The originally released Exchange 2000 patch has been determined
   to contain a regression error that can cause performance
   problems on the servers it is installed on. We have eliminated
   the regression error and updated the patch; we recommend that
   customers who installed the original patch install the updated
   one.

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 (tharbadkaotik.org)

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