Windows Server 2019 must prevent NTLM from falling back to a Null session.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-205917 | WN19-SO-000270 | SV-205917r991589_rule | Medium |
| Description |
| NTLM sessions that are allowed to fall back to Null (unauthenticated) sessions may gain unauthorized access. |
| STIG | Date |
| Microsoft Windows Server 2019 Security Technical Implementation Guide | 2025-01-15 |
Details
| Check Text (C-6182r356113_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-6182r356114_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". |