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Microsoft Security Bulletin (MS00-067)

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



Re-release: Patch Available for "Windows 2000 Telnet Client NTLM

Authentication" Vulnerability



Originally posted: September 14, 2000

Re-Released: September 21, 2000



Summary

=======

On September 14, 2000, Microsoft released the original version of

this bulletin, which was revised the following day to advise of a

problem with the patch. On September 21, 2000, a new version of the

patch was released, and the bulletin was updated to advise of its

availability. Microsoft recommends that all customers, including

those who applied the original version of the patch, apply the new

version.



The patch eliminates a security vulnerability in the telnet client

that ships with Microsoft(r) Windows 2000. The vulnerability could,

under certain circumstances, allow a malicious user to obtain

cryptographically protected logon credentials from another user.



Frequently asked questions regarding this vulnerability and

the patch can be found at

http://www.microsoft.com/technet/security/bulletin/fq00-067.asp



Issue

=====

Windows 2000 includes a telnet client capable of using NTLM

authentication when connecting to a remote NTLM enabled telnet

server. A vulnerability exists because the client will, by default,

perform NTLM authentication when connecting to the remote telnet

server. This could allow a malicious user to obtain another user's

NTLM authentication credentials without the user's knowledge.



A malicious user could exploit this behavior by creating a

carefully-crafted HTML document that, when opened, could attempt to

initiate a Telnet session to a rogue telnet server - automatically

passing NTLM authentication credentials to the malicious server's

owner. The malicious user could then use an offline brute force

attack to derive the password or, with specialized tools, could

submit a variant of these credentials in an attempt to access

protected resources.



This vulnerability would only provide the malicious user with the

cryptographically protected NTLM authentication credentials of

another user. It would not, by itself, allow a malicious user to gain

control of another user's computer. In order to leverage the NTLM

credentials (or subsequently cracked password), the malicious user

would have to be able to remotely logon to the target system.

However, best practices dictate that remote logon services be blocked

at border devices, and if these practices were followed, they would

prevent an attacker from using the credentials to logon to the target

system. Best practices also strongly recommend that Windows 2000

users logon to their hosts with User level credentials, and if these

practices were followed, they would prevent a malicious user from

obtaining Administrator level NTLM credentials.



Affected Software Versions

==========================

 - Microsoft Windows 2000



Patch Availability

==================

 - Microsoft Windows 2000:

   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=24399



Note: Customers who applied the original version of the patch should

consider applying the current version.  The original version

eliminated the vulnerability; however, if a malicious user attempted

to exploit the vulnerability, the patch caused the Telnet client to

fail. The current version of the patch eliminates the vulnerability

without interfering with Telnet connections.



Note: This patch will also be included in the next Service Pack for

Windows 2000. It can be applied to computers with or without Service

Pack 1.



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 MS00-067,

   http://www.microsoft.com/technet/security/bulletin/fq00-067.asp

 - Microsoft Knowledge Base (KB) article Q272743,

   http://www.microsoft.com/technet/support/kb.asp?ID=272743

 - 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

Product Support Services is available at

http://support.microsoft.com/support/contact/default.asp.



Acknowledgments

===============

Microsoft thanks  DilDog of @Stake Inc. (www.atstake.com) for

reporting this issue to us and working with us to protect customers.



Revisions

=========

 - September 14, 2000: Bulletin Created.

 - September 15, 2000: Bulletin re-released to advise of problem with

patch.

 - September 21, 2000: Bulletin re-released to advise of availability

of new patch.



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



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"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL

WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF

MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT

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THE FOREGOING LIMITATION MAY NOT APPLY.



September 21, 2000



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





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