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Q214840: MSV1_0 Allows Network Connections for Specific Accounts

Article: Q214840
Product(s): Microsoft Windows NT
Version(s): winnt:4.0 SP4
Operating System(s): 
Keyword(s): kbWinNT400sp5fix
Last Modified: 16-MAY-2002

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0 SP4 
- Microsoft Windows NT Server, Enterprise Edition version 4.0 SP4 
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SYMPTOMS
========

A problem occurs in Windows NT 4.0 Service Pack 4 when a user has changed the
password for his or her Windows NT domain account from a LanManager client (such
as a Windows for Workgroups or the Macintosh desktop). After the user's password
is changed from the LanManager client, that account may be used to log on
interactively and to make network connections from other systems using a blank
password.

The security problem does not affect user accounts where the password change is
initiated from Windows 95, Windows 98, or Windows NT systems. Furthermore, user
account password changes can only be initiated by the user who knows the current
password for the account. There is no opportunity for an unauthorized user to
change the password of another user account.

CAUSE
=====

LanManager remote file access clients on Windows for Workgroups, Macintosh, or
OS/2 use a different change password protocol than Windows NT, Windows 95, or
Windows 98 systems. The older password change protocol for these clients uses
only the "LM hash" form of the password for authentication. The Windows NT
domain controller stores only the LM hash form of the password credentials for
that user in the security account manager (SAM) database. The "NT hash" form of
the password for the user account is set to a NULL value.

The problem introduced in Windows NT 4.0 Service Pack 4 is a logic error in
validating network authentication for users with the NULL value for the NT hash
of the password. The result is that a network connection to a server can be made
from Windows 95, Windows 98, or Windows NT systems for those accounts using a
blank password.

RESOLUTION
==========

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or
the individual software update. For information on obtaining the latest service
pack, please go to:

- http://www.microsoft.com/Windows/ServicePacks/

-or-

- Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft
Product Support Services. For a complete list of Microsoft Product Support
Services phone numbers and information on support costs, please go to the
following address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

This hotfix has been posted to the following Internet location:

ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP4/Msv1-fix/



STATUS
======

Microsoft has confirmed this problem could result in some degree of security
vulnerability in Windows NT version 4.0 Service Pack 4. This problem was first
corrected in Windows NT version 4.0 Service Pack 5.

Additional query words: 4.00 sp4 lanman

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Keywords          : kbWinNT400sp5fix 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTSEntSearch kbWinNTSEnt400sp4 kbWinNTS400sp4 kbWinNTS400search
Version           : winnt:4.0 SP4
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

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