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Title:      Malformed Data Transfer Request can Cause Windows SMTP
            Service to Fail
Date:       27 February 2002
Software:   Microsoft Windows 2000; Microsoft Windows XP Professional
            Microsoft Exchange 2000
Impact:     Denial of Service
Max Risk:   Low
Bulletin:   MS02-012

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS02-012.asp.
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Issue:
======
An SMTP service installs by default as part of Windows 2000 server
products. Exchange 2000, which can only be installed on Windows 2000,
uses the native Windows 2000 SMTP service rather than providing its
own. In addition, Windows 2000 and Windows XP workstation products
provide an SMTP service that is not installed by default. All of
these implementations contain a flaw that could enable denial of
service attacks to be mounted against the service. 

The flaw involves how the service handles a particular type of SMTP
command used to transfer the data that constitutes an incoming
mail. By sending a malformed version of this command, an attacker
could cause the SMTP service to fail. This would have the effect
of disrupting mail services on the affected system, but would not
cause the operating system itself to fail.

Mitigating Factors:
====================
 - Windows XP Home Edition does not provide an SMTP service, and
   is not affected by the vulnerability. 

 - Windows 2000 Professional and Windows XP Professional do provide
   an SMTP service, but it is not installed by default. 

 - Windows 2000 server products do install the SMTP service by
   default. However, best practices recommend disabling any
   unneeded services, and systems on which the SMTP service had been
   disabled would not be at risk. 

 - Exchange 5.5, even if installed on a Windows 2000 server, is not
   affected by the vulnerability. 

 - The result of an attack would be limited to disrupting the SMTP
   service and, depending on the system configuration, potentially
   IIS and other internet services as well. However, it would not
   disrupt any other system functions. 

 - The vulnerability would not enable an attacker to gain any
   privileges on the affected system or to access users' email or
   data.

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

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-012.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 -  H D Moore (hdm@secureaustin.com)

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