Integrity Checking on Secure Channels with Domain Controllers

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0
• Microsoft Windows NT Server version 4.0, Terminal Server Edition

SYMPTOMS

When a Windows NT system joins a domain, a machine account is created. Thereafter, when the system boots, it uses the password for that account to create a secure channel with the domain controller for its domain. Requests sent on the secure channel are authenticated, and sensitive information (such as passwords) is encrypted, but the channel is not integrity checked.

Lack of integrity checking means that it is possible for an attacker who can intercept and modify requests to modify information in requests or responses undetected.

Use of such an attack to modify group membership information could allow an attacker who has interactive logon access to a workstation to become administrator on that workstation.

RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, please see the following article in the Microsoft Knowledge Base:

Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

MORE INFORMATION

A fix to Windows NT 4.0 Netlogon service has been designed that will allow for integrity checking. After applying this fix, the following Registry values can be used to modify the behavior of the secure channel between the client and domain controller. All of the following values can be found in the registry under the following key:


HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\netlogon\parameters

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" online Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" online Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

   SignSecureChannel

      Value Type: REG_DWORD - Boolean
      Valid Range: 0 (FALSE) or 1 (TRUE)
      Default: TRUE
      Description: This parameter specifies that all outgoing secure
                   channel traffic should be signed. If SealSecureChannel
                   is also TRUE, it will override any setting for this
                   parameter and force it to TRUE.

   SealSecureChannel

      Value Type: REG_DWORD - Boolean
      Valid Range: 0 (FALSE) or 1 (TRUE)
      Default: TRUE
      Description: This parameter specifies that all outgoing secure
                   channel traffic should be encrypted.

   RequireSignOrSeal

      Value Type: REG_DWORD - Boolean
      Valid Range: 0 (FALSE) or 1 (TRUE)
      Default: FALSE
      Description: This parameter specifies that all outgoing secure
                   channel traffic must be either signed or sealed. Without
                   this parameter, this is negotiated with the Domain
                   Controller. This flag should only be set if ALL of the
                   domain controllers in ALL the trusted domains support
                   signing and sealing. If this parameter is TRUE,
                   SignSecureChannel is implied to be TRUE. 

STATUS

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

Additional query words: 4.00

Keywords : NT4SP4Fix kbbug4.00 kbfix4.00.sp4 NTSrvWkst
Version : WinNT:4.0
Platform : winnt
Issue type : kbbug