NTLM must be prevented from falling back to a Null session.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-21952	WN08-SO-000062	SV-48422r2_rule	ECSC-1	Medium

Description
NTLM sessions that are allowed to fall back to Null (unauthenticated) sessions may gain unauthorized access.

STIG	Date
Windows 8 / 8.1 Security Technical Implementation Guide	2016-06-08

Details

Check Text ( C-45091r2_chk )
Analyze the system using the Security Configuration and Analysis snap-in. (See "Performing Analysis with the Security Configuration and Analysis Snap-in" in the STIG Overview document.) Expand the Security Configuration and Analysis tree view. Navigate to Local Policies -> Security Options. If the value for "Network Security: Allow LocalSystem NULL session fallback" is not set to "Disabled", this is a finding. The policy referenced configures the following registry value: Registry Hive: HKEY_LOCAL_MACHINE Subkey: \System\CurrentControlSet\Control\LSA\MSV1_0\ Value Name: allownullsessionfallback Type: REG_DWORD Value: 0

Check Text ( C-45091r2_chk )

Analyze the system using the Security Configuration and Analysis snap-in. (See "Performing Analysis with the Security Configuration and Analysis Snap-in" in the STIG Overview document.)
Expand the Security Configuration and Analysis tree view.
Navigate to Local Policies -> Security Options.

If the value for "Network Security: Allow LocalSystem NULL session fallback" is not set to "Disabled", this is a finding.

The policy referenced configures the following registry value:

Registry Hive: HKEY_LOCAL_MACHINE
Subkey: \System\CurrentControlSet\Control\LSA\MSV1_0\

Value Name: allownullsessionfallback

Type: REG_DWORD
Value: 0

Fix Text (F-41553r1_fix)
Configure the policy value for Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options -> "Network Security: Allow LocalSystem NULL session fallback" to "Disabled".