The service principal name (SPN) target name validation level must be turned off.

From Windows Server 2012/2012 R2 Domain Controller Security Technical Implementation Guide

Part of SPN Target Name Validation Level

Associated with: CCI-000366

SV-53175r1_rule The service principal name (SPN) target name validation level must be turned off.

Vulnerability discussion

If a service principle name (SPN) is provided by the client, it is validated against the server's list of SPNs. Implementation may disrupt file and print sharing capabilities.

Check content

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\Services\LanmanServer\Parameters\ Value Name: SmbServerNameHardeningLevel Type: REG_DWORD Value: 0

Fix text

Configure the policy value for Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options -> "Microsoft network server: Server SPN target name validation level" to "Off".

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