Windows Server 2019 must prevent NTLM from falling back to a Null session.

Documentable No

Rule ID SV-205917r991589_rule

CCI References

CCI-000366

Discussion

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

Check Procedure

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 Action

Configure the policy value for Computer Configuration >> Windows Settings >> Security Settings >> Local Policies >> Security Options >> "Network security: Allow LocalSystem NULL session fallback" to "Disabled".