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Title:      Unchecked Buffer in MSN Chat Control Can Lead to Code
            Execution (Q321661)
Date:       08 May 2002
Software:   MSN Chat, MSN Messenger, Exchange Instant Messenger
Impact:     Run Code of Attacker's Choice
Max Risk:   Critical
Bulletin:   MS02-022

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS02-022.asp.
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Issue:
======
The MSN Chat control is an ActiveX control that allows groups of
users to gather in a single, virtual location online to engage in
text messaging. The control is offered for download as a single
ActiveX control from a number of MSN sites. In addition, it is
included with MSN Messenger since version 4.5 and Exchange Instant
Messenger. While the MSN Chat control is included with these
products it is not used to provide Instant Messaging functionality,
but rather to add chat functionality to those products. 

An unchecked buffer exists in one of the functions that handles
input parameters in the MSN Chat control. A security
vulnerability results because it is possible for a malicious user
to levy a buffer overrun attack and attempt to exploit this flaw.
A successful attack could allow code to run in the user's context. 

It would be possible for an attacker to attempt to exploit
this vulnerability either through a malicious web site or through
HTML email. However, Outlook Express 6.0 and the
Outlook Email Security Update, which is available for
Outlook 98 and Outlook 2000, Outlook 2002 and can thwart such
attempts through their default security settings.

Mitigating Factors:
====================
 - A successful attack would require that the user have installed
   the MSN Chat control, MSN Messenger, or
   Exchange Instant Messenger. 

 - The MSN Chat control does not install with any version of
   Windows or Internet Explorer by default.
 
 - Windows Messenger which ships with Windows XP does not
   include the MSN Chat control. Windows XP users would be
   vulnerable only if they have chosen to install the MSN Chat
   control from MSN sites. 

 - The HTML email attack vector is blocked by the following
   Microsoft mail products: 
    - Outlook 98 and Outlook 2000 with the 
      Outlook Email Security Update
    - Outlook 2002
    - Outlook Express. 
   This is because these products all open HTML email in the
   Restricted Sites zone by default.

Risk Rating:
============
 - Internet systems: Low
 - Intranet systems: Low
 - Client systems: Critical

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-022.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - eEye Digital Security (http://www.eeye.com)

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