Microsoft Security Bulletin (MS00-043)

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Microsoft Security Bulletin (MS00-043)
- --------------------------------------

Patch Available for "Malformed E-mail Header" Vulnerability

Originally posted: July 18, 2000
Updated: July 20, 2000

Summary
=======
On July 18, 2000, Microsoft released the original version of this
bulletin, to advise customers of the issue and recommend that they
install either of the two service packs that will eliminate the
vulnerability. On July 20, 2000, the bulletin was updated to announce
the availability of patches that eliminate the vulnerability.

Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Outlook(r) and Outlook Express. Under
certain conditions, the vulnerability could allow a malicious user to
cause code of his choice to execute on another user's computer.

The patch eliminates this vulnerability as well as those discussed in
Microsoft Security Bulletins MS00-045 and MS00-046. Customers who
already have taken the corrective action discussed in either of these
bulletins do not need to take any additional action.

Frequently asked questions regarding this vulnerability and
the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-043.asp

Issue
=====
A component shared by Outlook and Outlook Express, Inetcomm.dll,
contains an unchecked buffer in the functionality that parses e-mail
headers when downloading mail via either POP3 or IMAP4. By sending an
e-mail that overruns the buffer, a malicious user could cause either
of two effects to occur when the mail was downloaded from the server
by an affected e-mail client:
 - If the affected field were filled with random data, the
   e-mail could be made to crash.
 - If the affected field were filled with carefully-crafted data,
   the e-mail client could be made to run code of the malicious
   user's choice.

The vulnerability affects all Outlook Express users and all Outlook
users whose mail clients are configured to use either POP3 or IMAP4.
Outlook users who have configured Outlook to use only MAPI services
are unlikely to be affected by the vulnerability. Despite this,
Microsoft recommends that such customers apply one of the corrective
steps discussed in the Patch Availability section, primarily because
the patch protects against other vulnerabilities that affect all
Outlook users, regardless of the mail protocol they use.

A version of Inetcomm.dll that is not affected by the vulnerability
ships as part of Outlook Express 5.5, and customers who have
installed it do not need to take any additional action. Outlook
Express 5.5 is available as part of Internet Explorer 5.01 Service
Pack 1, and, except when installed on Windows 2000, Internet Explorer
5.5. Customers who do not wish to upgrade to Outlook Express 5.5
should install the patch provided below.

Affected Software Versions
==========================
 - Microsoft Outlook Express 4.0
 - Microsoft Outlook Express 4.01
 - Microsoft Outlook Express 5.0
 - Microsoft Outlook Express 5.01
 - Microsoft Outlook 97
 - Microsoft Outlook 98
 - Microsoft Outlook 2000

Patch Availability
==================
This vulnerability can be eliminated by taking any of the following
actions:
 - Installing the patch available at
   http://www.microsoft.com/windows/ie/download/critical/patch9.htm
 - Performing a default installation of Internet Explorer 5.01
   Service Pack 1,
   http://www.microsoft.com/Windows/ie/download/ie501sp1.htm.
 - Performing a default installation of Internet Explorer 5.5
   (http://www.microsoft.com/windows/ie/download/ie55.htm)
   on any system except Windows 2000.

Note: The patch requires IE 4.01 SP2
(http://www.microsoft.com/windows/ie/download/ie401sp2.htm) or
IE 5.01 (http://www.microsoft.com/windows/ie/download/ie501.htm)
to install. Customers who install this patch on versions other
than these may receive a message reading "This update does not
need to be installed on this system". This message is incorrect.
More information is available in KB article Q267884

Note: In addition to eliminating the vulnerability at issue
here, the steps above also eliminate all vulnerabilities
discussed in Microsoft Security Bulletins MS00-045
(http://www.microsoft.com/technet/security/bulletin/MS00-045.asp)
and MS00-046
(http://www.microsoft.com/technet/security/bulletin/MS00-046.asp).
Customers who already have taken the corrective action discussed
in either of these bulletins do not need to take any additional
action.

Note: Additional security patches are available at the Microsoft
Download Center (http://www.microsoft.com/downloads).

More Information
================
Please see the following references for more information related to
this issue.
 - Frequently Asked Questions: Microsoft Security Bulletin MS00-043,
   http://www.microsoft.com/technet/security/bulletin/fq00-043.asp
 - Microsoft Knowledge Base article Q267884 discusses this issue
   and will be available soon.
 - Microsoft TechNet Security web site,
   http://www.microsoft.com/technet/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.

Revisions
=========
 - July 18, 2000: Bulletin Created.
 - July 20, 2000: Bulletin updated to announce availability of a
   patch that does not require a full version upgrade of
   Internet Explorer.

- ----------------------------------------------------------------

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Last Updated July 20,2000

(c) 2000 Microsoft Corporation. All rights reserved. Terms of use.

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