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Microsoft Security Bulletin (MS00-047)
- --------------------------------------

Patch Available for "NetBIOS Name Server Protocol Spoofing"
Vulnerability
Originally Posted: July 27, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in a protocol implemented in Microsoft(r) Windows(r)
systems. It could be used to cause a machine to refuse to respond to
requests for service.

Frequently asked questions regarding this vulnerability and the patch
can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-047.asp

Issue
=====
The NetBIOS Name Server (NBNS) protocol, part of the NetBIOS over
TCP/IP (NBT) family of protocols, is implemented in Windows systems
as the Windows Internet Name Service (WINS). By design, NBNS allows
network peers to assist in managing name conflicts. Also by design,
it is an unauthenticated protocol and therefore subject to spoofing.
A malicious user could misuse the Name Conflict and Name Release
mechanisms to cause another machine to conclude that its name was in
conflict. Depending on the scenario, the machine would as a result
either be unable to register a name on the network, or would
relinquish a name it already had registered. The result in either
case would be the same - the machine would not respond requests sent
to the conflicted name anymore.

If normal security practices have been followed, and port 137 UDP has
been blocked at the firewall, external attacks would not be possible.
A patch is available that changes the behavior of Windows systems in
order to give administrators additional flexibility in managing their
networks. The patch allows administrators to configure a machine to
only accept a name conflict datagram in direct response to a name
registration attempt, and to configure machines to reject all name
release datagrams. This will reduce but not eliminate the threat of
spoofing. Customers needing additional protection may wish to
consider using IPSec in Windows 2000 to authenticate all sessions on
ports 137-139.

Affected Software Versions
==========================
 - Microsoft Windows NT 4.0 Workstation
 - Microsoft Windows NT 4.0 Server
 - Microsoft Windows NT 4.0 Server, Enterprise Edition
 - Microsoft Windows NT 4.0 Server, Terminal Server Edition
 - Microsoft Windows 2000

Patch Availability
==================
 - Windows 2000:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=23370
 - Windows NT 4.0 Workstation, Server, and Server, Enterprise
   Edition:Patch to be released shortly.
 - Windows NT 4.0 Server, Terminal Server Edition: Patch to be
   released shortly.

Note Additional security patches are available at the Microsoft
Download Center

More Information
================
Please see the following references for more information related to
this issue.
 - Frequently Asked Questions: Microsoft Security Bulletin MS00-047,
   http://www.microsoft.com/technet/security/bulletin/fq00-047.asp
 - Microsoft Knowledge Base article Q269239 discusses this issue
   and will be available soon.
 - Protocol Standard for a NetBIOS Service on a TCP/UDP Transport:
   Concepts and Methods, RFC 1001.
 - Protocol Standard for a NetBIOS Service on a TCP/UDP Transport:
   Detailed Specification, RFC 1002.
 - 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.

Acknowledgments
===============
Microsoft thanks  the following customers for working with us to
protect customers:

COVERT Labs at PGP Security, Inc., for reporting the unsolicited
NetBIOS Name Conflict datagram issue to us.
Sir Dystic of Cult of the Dead Cow for reporting the Name Release
issue to us.

Revisions
=========
July 27, 2000: Bulletin Created.

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

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Last Updated July 27, 2000
(c) 2000 Microsoft Corporation. All rights reserved. Terms of use.

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