Windows Server 2019 Internet Protocol version 6 (IPv6) source routing must be configured to the highest protection level to prevent IP source routing.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
low	V-205858	SRG-OS-000480-GPOS-00227	WN19-CC-000030	SV-205858r991589_rule	2025-02-25	3

Description
Configuring the system to disable IPv6 source routing protects against spoofing.

ℹ️ Check
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\Tcpip6\Parameters\ Value Name: DisableIPSourceRouting Type: REG_DWORD Value: 0x00000002 (2)

✔️ Fix
Configure the policy value for Computer Configuration >> Administrative Templates >> MSS (Legacy) >> "MSS: (DisableIPSourceRouting IPv6) IP source routing protection level (protects against packet spoofing)" to "Enabled" with "Highest protection, source routing is completely disabled" selected. This policy setting requires the installation of the MSS-Legacy custom templates included with the STIG package. "MSS-Legacy.admx" and "MSS-Legacy.adml" must be copied to the \Windows\PolicyDefinitions and \Windows\PolicyDefinitions\en-US directories respectively.

✔️ Fix

Configure the policy value for Computer Configuration >> Administrative Templates >> MSS (Legacy) >> "MSS: (DisableIPSourceRouting IPv6) IP source routing protection level (protects against packet spoofing)" to "Enabled" with "Highest protection, source routing is completely disabled" selected. This policy setting requires the installation of the MSS-Legacy custom templates included with the STIG package. "MSS-Legacy.admx" and "MSS-Legacy.adml" must be copied to the \Windows\PolicyDefinitions and \Windows\PolicyDefinitions\en-US directories respectively.