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Q301361: XGEN: Incorrect Attachment Processing in Exchange Server 5.5 OWA

Article: Q301361
Product(s): Microsoft Exchange
Version(s): 5.5,5.5 SP1,5.5 SP2,5.5 SP3,5.5 SP4
Operating System(s): 
Keyword(s): kbExchange550preSP5fix
Last Modified: 08-MAY-2002

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The information in this article applies to:

- Microsoft Exchange Server, versions 5.5, 5.5 SP1, 5.5 SP2, 5.5 SP3, 5.5 SP4 
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For additional information about a similar problem that can occur in Exchange 2000 Server, click the article number below to view the article in the Microsoft Knowledge Base:

  Q299535 XGEN: Incorrect Attachment Processing in Exchange 2000 Outlook Web
  Access Can Run Script

SYMPTOMS
========

Microsoft Outlook Web Access (OWA) is a service of Exchange Server 5.5 and
Exchange 2000 Server that a user can use to gain access to an Exchange mailbox
by using a Web browser. However, vulnerability exists in the interaction between
OWA and Microsoft Internet Explorer for message attachments. If an attachment
contains Hypertext Markup Language (HTML) code that includes script, the script
is run when the user opens the attachment, regardless of the attachment type.
Because OWA requires that scripting be enabled in the zone where the OWA server
is located, this script can take action against the user's Exchange mailbox.

An attacker might use this vulnerability to construct an attachment that contains
malicious script code. The attacker can then send the attachment in a message to
a user. If the user opens the attachment in OWA, the script runs and can take
action against the user?s mailbox as if the script is the user, including, under
certain circumstances, manipulation of messages or folders.

The following are mitigating factors:

- The vulnerability can only be exploited if the user is using OWA in
  conjunction with Internet Explorer.

- The vulnerability can only be exploited by attachments that are received by
  using OWA. In general, an attacker has no way to determine whether a user
  will open an attachment by using OWA rather than Microsoft Outlook.

- An attacker's ability to exploit this vulnerability requires that the
  attacker entice the user to open an attachment from an untrusted source. The
  best practice is not to open any attachment from an unknown or untrusted
  source.

RESOLUTION
==========

A supported fix is now available from Microsoft, but it is only intended to
correct the problem described in this article and should be applied only to
systems that are determined to be at risk of attack. Please evaluate your
computer's physical accessibility, network and Internet connectivity, and other
factors to determine the degree of risk to your computer. Please see the
associated Microsoft Security Bulletin
(http://www.microsoft.com/technet/security/bulletin/MS01-030.asp) to help make
this determination. This fix may receive additional testing at a later time, to
further ensure product quality. If your computer is sufficiently at risk,
Microsoft recommends that you apply this fix now. Otherwise, wait for the next
Microsoft Exchange Server 5.5 service pack that contains this fix.

To resolve this problem immediately, download the fix as instructed below or
contact Microsoft Product Support Services to obtain the fix. For a complete
list of Microsoft Product Support Services phone numbers and information on
support costs, please go to the following address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are normally incurred for support calls may
be canceled, if a Microsoft Support Professional determines that a specific
update will resolve your problem. Normal support costs will apply to additional
support questions and issues that do not qualify for the specific update in
question.

The following files are available for download from the Microsoft Download
Center:

  DownloadDownload Q301361i386.exe now
  (http://www.microsoft.com/Downloads/Release.asp?ReleaseID=30568)

Release Date: June 8, 2001

For additional information about how to download Microsoft Support files, click
the article number below to view the article in the Microsoft Knowledge Base:

  Q119591 How to Obtain Microsoft Support Files from Online Services

Microsoft used the most current virus detection software available on the date of
posting to scan this file for viruses. After it is posted, the file is housed on
secure servers that prevent any unauthorized changes to the file.

The English version of this fix should have the following file attributes or
later:

Component: OWA

+---------------------+
| File name | Version | 
+---------------------+
| Read.asp  | na      | 
+---------------------+

NOTES

- Because of file dependencies, this fix requires Microsoft Exchange Server
  version 5.5 Service Pack 4.

- You need to apply this fix to all servers that run the OWA components. With
  Exchange Server 5.5, you can install the OWA components on a computer that is
  separate from the Exchange Server. If you install OWA separately, you need to
  run this patch on the separate computer.

- Sometimes, after applying this fix, users may get a blank window when they
  open their messages using OWA. If this occurs, please review the following
  Knowledge Base article

  Q314532 XWEB: Troubleshooting Blank Message Bodies in Outlook Web



STATUS
======

Microsoft has confirmed that this problem could result in some degree of
security vulnerability in Microsoft Exchange Server version 5.5.

MORE INFORMATION
================

For more information about this security vulnerability, see the following
Microsoft Web site:

  http://www.microsoft.com/technet/security/bulletin/MS01-030.asp

Additional query words: security_patch

======================================================================
Keywords          : kbExchange550preSP5fix 
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2 kbExchange550SP1 kbExchange550SP2 kbExchange550SP3 kbExchange550SP4
Version           : :5.5,5.5 SP1,5.5 SP2,5.5 SP3,5.5 SP4
Issue type        : kbbug
Solution Type     : kbfix

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