Allow NTLM to fall back to NULL session when used with LocalSystem. The default is TRUE up to Windows Vista and FALSE in Windows 7. Vulnerability: NULL sessions are less secure because by definition they are unauthenticated. Counter Measure: Configure Network security: Allow LocalSystem NULL session fallback to Disabled. Potential Impact: Any applications that require NULL sessions for LocalSystem will not work as designed. Fix: (1) GPO: Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options\Network security: Allow LocalSystem NULL session fallback (2) REG: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Lsa\MSV1_0!allownullsessionfallback