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CERT Coordination Center

Microsoft Windows 2000 Workstation in mixed-mode domain may ignore domain account lockout restriction due to flaw in NTLM authentication

Vulnerability Note VU#818496

Original Release Date: 2001-05-01 | Last Revised: 2001-06-26


A flaw in certain configurations of Windows 2000 can allow an intruder to make an unlimited number of guesses to attempt to determine a password, despite policies intended to limit the number of guesses.


Domain administrators can set policies governing certain aspects of behavior within a domain. One of the policies that can be set is the number of failed password attempts before the account will be locked out. This is intended to prevent an intruder from attempting to guess a password through brute force. Under some circumstances, described in detail in Microsoft Security Bulletin MS-089, the policy can be circumvented, allowing an intruder to make repeated unlimited attempts to guess a password. The policy would be enforced relative to attempts to authenticate to the domain, but not relative to cached credentials.


An intruder can attempt to guess (possibly in an automated fashion) passwords on a Windows 2000 machine.


Apply the patches and workarounds described in

Vendor Information


Microsoft Affected

Updated:  April 30, 2001



Vendor Statement


Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

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Our thanks to Microsoft for the information contained in their advisory, and to Finch Brett, who reported the information to Microsoft.

This document was written by Shawn V. Hernan.

Other Information

CVE IDs: None
Severity Metric: 3.15
Date Public: 2000-11-21
Date First Published: 2001-05-01
Date Last Updated: 2001-06-26 02:19 UTC
Document Revision: 9

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