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Local System Account and Null Sessions in Windows NT

This article was previously published under Q132679
This article discusses the Local System account and its securityimplications, as well as a useful way to run applications in Local Systemsecurity context.


The shell application, which is typically Progman.exe, runs under the Domain\Usersecurity context. Most processes that start from the shell process inherit the same security context.

When you set up Windows NT services, you choose a security contextfor the service to be started under (because these services are typicallynot started by a user). To check the security being used by a service:
  1. Click Start, click Run, type control panel, and then double click Services.
  2. Select a service, and then click Startup.
The security context of the service is set in the Log On As window pane.

Services Using The System Account

Services that use the system account start in the system context (withoutcredentials). In Windows NT 3.5 and later, Windows NT services with nocredentials (no domain name, user name, or password) that attempt toconnect to network resources are denied access because they have nocredentials and they are using a null session.For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
122702 Using the System Account as a Service in Windows NT 3.5
NOTE: System Account and This Account: Local System use the same account.

A null session is only established when there are no credentials for aprocess to start under (no user name or password). Typically, only theoperating system itself runs as system.

On the local computer, the operating system is known as:
   Default Owner:   Administrators    local group   User:            System            pseudo group - local group scope   Groups:          Administrators    local group                    Everyone          pseudo group - local group scope				

When this context is used to access the network, a null session is used.This produces the following context on remote computers:
   Default Owner:   Everyone   User:            Everyone   Groups:          AnonymousLogon    pseudo group - local group scope                    Network           pseudo group - local group scope				

Only three identifiers can provide the null session access (Everyone,AnonymousLogon, and Network). The local system context and null sessioncontext have only the identifier Everyone in common. To configure WindowsNT so that a service can access objects on its own computer directly, aswell as over the network, use the Everyone identifier.

The default owners of these two contexts (as well as their default DACLs)are different. Any files you created in these contexts will be owned byAdministrators. Any files you create through a null session will be ownedby Everyone.

prodnt localsystem username

Article ID: 132679 - Last Review: 11/01/2006 04:55:00 - Revision: 2.1

  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Advanced Server 3.1
  • kbusage KB132679