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Microsoft Security Bulletin (MS99-027)
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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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