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Title:      Invalid RDP Data can Cause Terminal Service Failure
Date:       18 October 2001
Revised:    22 October 2001 (version 2.0)
Software:   Windows NT 4.0 Server, Terminal Server Edition,
            Windows 2000 Server and Advanced Server
Impact:     Denial of service
Max Risk:   Moderate
Bulletin:   MS01-052

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS01-052.asp.
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Reason for Revision:
====================
On October 18, 2001 Microsoft released the original version of this
bulletin. On October 19, 2001, an issue was identified with the
Windows 2000 patch. The patch was withdrawn so that it could be
updated and re-released. On October 22, 2001 the updated patch
and bulletin were posted. 

We recommend that customers who installed the original version
of the Windows 2000 patch install the updated version.
 
Issue:
======
The implementation of the Remote Data Protocol (RDP) in the terminal
service in Windows NT  4.0 and Windows 2000 does not correctly handle
a particular series of data packets. If such  a series of packets
were received by an affected server, it would cause the server to
fail.  The server could be put back into normal service by rebooting
it, but any work in progress  at the time of the attack would be
lost. 

It would not be necessary for an attacker to be able to start a
session with an affected  server in order to exploit this
vulnerability - the only prerequisite would be the need to  be able
to send the correct series of packets to the RDP port on the server. 

Mitigating Factors:
====================
 - There is no capability to breach the security of a terminal 
   server session via this vulnerability, or to add, change or
   delete data on the server. It is a denial of service 
   vulnerability only. 
 - The specific sequence of data packets involved in this 
   vulnerability cannot be generated as part of a legitimate 
   terminal server session. 

Risk Rating:
============
 - Internet systems: Low
 - Intranet systems: Moderate
 - Client systems: None

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms01-052.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Luciano Martins of Deloitte & Touche Argentina 
   (http://www.deloitte.com.ar) 

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