Title

NTLM must be prevented from falling back to a Null session. (Cat II impact)

Discussion

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

Check Content

Analyze the system using the Security Configuration and Analysis snap-in. 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 Registry Path: \SYSTEM\CurrentControlSet\Control\LSA\MSV1_0\ Value Name: allownullsessionfallback Type: REG_DWORD Value: 0

Fix Text

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

Additional Identifiers

Rule ID: SV-25275r2_rule

Vulnerability ID: V-21952

Group Title: NTLM NULL Session Fallback

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.