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

From Windows Server 2008 R2 Member Server Security Technical Implementation Guide

Associated with IA controls: ECSC-1

SV-32446r1_rule NTLM will be prevented from falling back to a Null session.

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This setting prevents NTLM from falling back to a Null (unauthenticated) session.

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

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