Windows Server 2025 must prevent NTLM from falling back to a Null session.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-278221 | WN25-SO-000270 | SV-278221r1181369_rule | CCI-000366 | medium |
| Description | ||||
| NTLM sessions that are allowed to fall back to Null (unauthenticated) sessions may gain unauthorized access. | ||||
| STIG | Date | |||
| Microsoft Windows Server 2025 Security Technical Implementation Guide | 2026-02-20 | |||
Details
Check Text (C-278221r1181369_chk)
If the following registry value does not exist or is not configured as specified, this is a finding:
Registry Hive: HKEY_LOCAL_MACHINE
Registry Path: \SYSTEM\CurrentControlSet\Control\LSA\MSV1_0\
Value Name: allownullsessionfallback
Type: REG_DWORD
Value: 0x00000000 (0)
Fix Text (F-82656r1181368_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".