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Microsoft Security Bulletin (MS00-089)

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

Patch Available for "Domain Account Lockout" Vulnerability

Originally posted: November 21, 2000



Summary

=======

Microsoft has released a patch that eliminates a security

vulnerability in Microsoft(r) Windows  2000. The vulnerability could

allow a malicious user to use repeated attempts to guess an account

password even if the domain administrator had set an account lockout

policy.



Frequently asked questions regarding this vulnerability and

the patch can be found at

http://www.microsoft.com/technet/security/bulletin/fq00-089.asp



Issue

=====

A flaw in the way that NTLM authentication operates in Windows 2000

could allow a domain account  lockout policy to be bypassed on a

local Windows 2000 machine, even if the domain administrator  had set

such a policy. The ability of a malicious user to avoid the domain

account lockout policy  could increase the threat from a brute force

password-guessing attack.



This vulnerability only affects Windows 2000 machines that are

members of non-Windows 2000  domains. In addition, the vulnerability

only affects domain user accounts that have previously  logged into

the target machine and already have cached credentials established on

that machine.  If a domain account lockout policy is in place and an

attacker attempts a brute force  password-guessing attack, the domain

user account will be locked out as expected at the domain

controller. However, if the attacker is able find the correct

password, the local Windows 2000  machine will log the attacker on

using cached credentials in violation of the account lockout  policy.

Although the attacker would be able to log on to the local machine,

he or she would not  be able to authenticate to the domain or gain

access to resources on other machines in the  domain.



Affected Software Versions

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

 - Microsoft Windows 2000 Professional, Service Pack 1

 - Microsoft Windows 2000 Server, Service Pack 1

 - Microsoft Windows 2000 Advanced Server, Service Pack 1

 - Microsoft Windows 2000 Datacenter, Service Pack 1



Note Windows 2000 Gold is not affected by this vulnerability.



Patch Availability

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

 - http://www.microsoft.com/Downloads/Release.asp?ReleaseID=25606



Note: Windows 2000 users connected to a Windows 2000 domain, stand

alone Windows 2000 machines,  and users of NT 4.0 do not need to take

any action.



Note: The Windows 2000 patch can be applied to systems running

Windows 2000 Service Pack 1. Users  of Windows 2000 Gold are not

affected and do not need to take any action. This patch will be

included in Windows 2000 Service Pack 2.



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 MS00-089,

   http://www.microsoft.com/technet/security/bulletin/fq00-089.asp

 - Microsoft Knowledge Base article Q274372 discusses this issue and

   will be available soon.

 - 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 Finch Brett (mailto:brett.finch@hrs.ualberta.ca),

Human Resources, University of  Alberta, for reporting this issue to

us and working with us to protect customers.



Revisions

=========

 -  November 21, 2000: Bulletin Created.



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

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