The service principal name (SPN) target name validation level must be configured to Accept if provided by client.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-21950	WN08-SO-000035	SV-48416r2_rule	ECSC-1	Medium

Description
If a service principle name (SPN) is provided by the client, it is validated against the server's list of SPNs, aiding in the prevention of spoofing.

STIG	Date
Windows 8/8.1 Security Technical Implementation Guide	2017-05-17

Details

Check Text ( C-45085r2_chk )
Analyze the system using the Security Configuration and Analysis snap-in. (See "Performing Analysis with the Security Configuration and Analysis Snap-in" in the STIG Overview document.) Expand the Security Configuration and Analysis tree view. Navigate to Local Policies -> Security Options. If the value for "Microsoft network server: Server SPN target name validation level" is not set to "Accept if provided by client", this is a finding. The policy referenced configures the following registry value: Registry Hive: HKEY_LOCAL_MACHINE Subkey: \System\CurrentControlSet\Services\LanmanServer\Parameters\ Value Name: SmbServerNameHardeningLevel Type: REG_DWORD Value: 1

Check Text ( C-45085r2_chk )

Analyze the system using the Security Configuration and Analysis snap-in. (See "Performing Analysis with the Security Configuration and Analysis Snap-in" in the STIG Overview document.)
Expand the Security Configuration and Analysis tree view.
Navigate to Local Policies -> Security Options.

If the value for "Microsoft network server: Server SPN target name validation level" is not set to "Accept if provided by client", this is a finding.

The policy referenced configures the following registry value:

Registry Hive: HKEY_LOCAL_MACHINE
Subkey: \System\CurrentControlSet\Services\LanmanServer\Parameters\

Value Name: SmbServerNameHardeningLevel

Type: REG_DWORD
Value: 1

Fix Text (F-41547r1_fix)
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 "Accept if provided by client".