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Q124184: Service Running as System Account Fails Accessing Network

Article: Q124184
Product(s): Microsoft Windows NT
Version(s): 3.5,4.0
Operating System(s): 
Keyword(s): kbKernBase kbSecurity kbFAQ KbSECVulnerability
Last Modified: 29-APR-2002

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The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.5, 4.0 
- Microsoft Windows NT Server versions 3.5, 4.0 
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SYMPTOMS
========

When an application is started using the system account, it logs on with null
credentials. If it attempts to access a remote Windows NT 3.5 server resource
(using a null session), it fails. Scheduler service scripts (AT command) and
other service or application operations attempting to access server resources
over the network receive errors such as the following:

  Error 5: Access is denied.

When an application using the system account uses a UNC name to access a shared
resource, the following error message is returned:

  File Not Found

NOTE: Scheduler service script error messages can be caught by redirecting the AT
command to a file.

CAUSE
=====

Services, including the Scheduler, use null session support when logged on as
system account to interact with desktop.

Windows NT version 3.1 supports null sessions by default. However, Windows NT
version 3.5 does not provide this support unless specifically configured to do
so. This change was made in order to provide a higher default level of
security.


When a process is running under the context of the system account, it attempts to
use a null session for credentials to acquire a resource access. AT scripts
performing commands, such as NET USE, will default to these credentials. A
protocol analyzer trace reveals the null session request associated with the
Server Message Block (SMB) Session Setup & X in which no explicit
credentials are passed.

RESOLUTION
==========

Do not use the system account. Services, such as Scheduler, and custom
applications can be configured using user-specific accounts. User-specific
accounts provide user level security based on a specific account and associated
password.

NOTE: For more information, see Chapter 15: Server Manager, Assigning a Logon
Account to the Schedule Service in the "Windows NT Server 3.5 System Guide."

If you desire null session support, you can modify the registry of each remote
resource computer as follows.

WARNINGS:

- A shared resource configured in this manner is not secure. Microsoft does not
  recommend this configuration if null session security is a consideration.

- Using the Registry Editor incorrectly can cause serious, system- wide
  problems that may require you to reinstall Windows NT to correct them.
  Microsoft cannot guarantee that any problems resulting from the use of the
  Registry Editor can be solved. Use this tool at your own risk.

1. Start the registry editor, REGEDT32.EXE

2. From the HKEY_LOCAL_MACHINE subtree, go to the following key:

     \System
       \CurrentControlSet
         \Services
           \LanmanServer
             \Parameters
               \NullSessionShares

  NOTE: NullSessionShares is type REG_MULTI_SZ

3. On a new line within the NullSessionShares key, type in the share you want to
  access with a null session (for example: "PUBLIC")

4. If your application uses Named Pipes and requires null session support.

  a. From the HKEY_LOCAL_MACHINE subtree, go to the following key:

        \System
          \CurrentControlSet
            \Services
              \LanmanServer
                \Parameters
                  \NullSessionPipes

     NOTE: NullSessionPipes is type REG_MULTI_SZ

  b. On a new line within the NullSessionShares key, type in the pipe you want
     to access with a null session.

5. Stop and restart the server.

For additional information, please see the following articles in the Microsoft
Knowledge Base:

  ARTICLE-ID: Q132679
  TITLE : Local System Account and Null Sessions in Windows NT

  ARTICLE-ID: Q122702
  TITLE : Using the System Account as a Service in Windows NT 3.5

  ARTICLE-ID: Q121281
  TITLE : LMHOSTS #Include Directives Requires Null Session Support

Additional query words: prodnt

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Keywords          : kbKernBase kbSecurity kbFAQ KbSECVulnerability 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS350 kbWinNTS350search
Version           : :3.5,4.0

=============================================================================

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