Network access: Restrict anonymous access to Named Pipes and Shares

Updated: November 15, 2012

Applies To: Windows 7, Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, Windows Vista, Windows XP

This security policy reference topic for the IT professional describes the best practices, location, values, policy management and security considerations for this policy setting.

Reference

This policy setting enables or disables the restriction of anonymous access to only those shared folders and pipes that are named in the Network access: Named pipes that can be accessed anonymously and Network access: Shares that can be accessed anonymously settings. The setting controls null session access to shared folders on your computers by adding RestrictNullSessAccess with the value 1 in the registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManServer\Parameters. This registry value toggles null session shared folders on or off to control whether the Server service restricts unauthenticated clients' access to named resources.

Null sessions are a weakness that can be exploited through the various shared folders on the computers in your environment.

Possible values

• Enabled

• Disabled

• Not defined

Best practices

1. Set this policy to Enabled. Enabling this policy setting restricts null session access to unauthenticated users to all server pipes and shared folders except those listed in the NullSessionPipes and NullSessionShares registry entries.

Location

GPO_name\Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options

Default values

The following table lists the actual and effective default values for this policy. Default values are also listed on the policy’s property page.

Operating system version differences

There are no differences in this security policy between Windows operating systems beginning with Windows Server 2003.

Policy management

This section describes features and tools that are available to help you manage this policy.

Restart requirement

None. Changes to this policy become effective without a computer restart when they are saved locally or distributed through Group Policy.

Security considerations

This section describes how an attacker might exploit a feature or its configuration, how to implement the countermeasure, and the possible negative consequences of countermeasure implementation.

Vulnerability

Null sessions are a weakness that can be exploited through shared folders (including the default shared folders) on computers in your environment.

Countermeasure

Enable the Network access: Restrict anonymous access to Named Pipes and Shares setting.

Potential impact

You can enable this policy setting to restrict null-session access for unauthenticated users to all server pipes and shared folders except those that are listed in the NullSessionPipes and NullSessionShares entries.

If you choose to enable this setting, and you are supporting Windows NT 4.0 domains, determine whether any of the named pipes in the following list are required to maintain trust relationships between the domains and then add the pipe to the Network access: Named pipes that can be accessed anonymously setting:

• COMNAP–SNA session access

• COMNODE–SNA session access

• SQL\QUERY–SQL instance access

• SPOOLSS–Spooler service

• LLSRPC–License Logging service

• Netlogon–Net Logon service

• Lsarpc–LSA access

• Samr–Remote access to SAM objects

• browser–Computer Browser service

In operating systems earlier than Windows Server 2003 with Service Pack 1 (SP1), these named pipes were allowed anonymous access by default. In later operating systems, these pipes must be explicitly added if needed.