Microsoft Security Bulletin (MS00-089)
Patch Available for "Domain Account Lockout" Vulnerability
Originally posted: November 21, 2000
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
Frequently asked questions regarding this vulnerability and
the patch can be found at
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
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.
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
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
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-089,
- Microsoft Knowledge Base article Q274372 discusses this issue and
will be available soon.
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Product Support Services is available at
Microsoft thanks Finch Brett (mailto:email@example.com),
Human Resources, University of Alberta, for reporting this issue to
us and working with us to protect customers.
- November 21, 2000: Bulletin Created.
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