Microsoft Security Bulletin (MS99-027)

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Microsoft Security Bulletin (MS99-027)
--------------------------------------

Patch Available for "Encapsulated SMTP Address" Vulnerability

Originally Posted: August 06, 1999

Summary
=======
Microsoft has released a patch that eliminates a security vulnerability in
Microsoft(r)  Exchange(r) Server. The vulnerability could allow an attacker
to perform mail relaying via an  Exchange server that is configured to act
as a gateway for other Exchange sites using the  Internet Messaging Service.

Frequently asked questions regarding this vulnerability can be
found at http://www.microsoft.com/security/bulletins/MS99-027faq.asp

Issue
=====
Exchange Server implements features designed to defeat "mail relaying", a
practice in which an  attacker causes an e-mail server to forward mail from
the attacker, as though the server were the  sender of the mail. However, a
vulnerability exists in this feature, and could allow an attacker  to
circumvent the anti-relaying features in an Internet-connected Exchange
Server.

The vulnerability lies in the way that site-to-site relaying is performed
via SMTP. Encapsulated  SMTP addresses could be used to send mail to any
desired e-mail address. The patch eliminates the  vulnerability by making
encapsulated SMTP addresses subject to the same anti-relay protections as
non-encapsulated SMTP addresses.

Affected Software Versions
==========================
 - Microsoft Exchange Server 5.5

Patch Availability
==================
 - ftp://ftp.microsoft.com/bussys/exchange/exchange-public
   /fixes/Eng/Exchg5.5/PostSP2/imc-fix

  NOTE: Line breaks have been inserted into the above URL for readability.

More Information
================
Please see the following references for more information related to this
issue.
 - Microsoft Security Bulletin MS99-027: Frequently Asked Questions,
   http://www.microsoft.com/security/bulletins/MS99-027faq.asp.
 - Microsoft Knowledge Base (KB) article Q237927,
   XIMS: Messages Sent to Encapsulated SMTP Address Are Rerouted
   Even Though Rerouting Is Disabled,
   http://support.microsoft.com/support/kb/articles/q237/9/27.asp.
 - Microsoft Security Advisor web site,
   http://www.microsoft.com/security/default.asp.

Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
http://support.microsoft.com/support/contact/default.asp.

Acknowledgments
===============
Microsoft acknowledges Laurent Frinking of Quark Deutschland GmbH for
bringing this issue to our  attention and working with us to alert customers
about it.

Revisions
=========
 - August 06, 1999: Bulletin Created.

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(c) 1999 Microsoft Corporation. All rights reserved.

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