MSV1_0 Incorrectly Allows Network Connections for Specific Accounts

ID: Q214840

The information in this article applies to:

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 fix. For information on obtaining the latest service pack, please go to:

For information on obtaining the individual fix, 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/support/supportnet/default.asp

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/
NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, a fee may be charged. This fee is refundable if it is determined that you only require the fix you requested. However, this fee is non-refundable if you request additional technical support, if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:
Q154871 Determining If You Are Eligible for No-Charge Technical Support


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 


Keywords          : kbbug4.00 kbfix4.00 nt4sp5fix 
Version           : winnt:4.0 SP4
Platform          : winnt 
Issue type        : kbbug

Last Reviewed: May 5, 1999