Windows Defender Firewall with Advanced Security local firewall rules must not be merged with Group Policy settings when connected to a public network.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-242004	SRG-OS-000327-GPOS-00127	WNFWA-000024	SV-242004r922958_rule	2023-08-23	2

Description
A firewall provides a line of defense against attack. To be effective, it must be enabled and properly configured. Local firewall rules will not be merged with Group Policy settings on a public network to prevent Group Policy settings from being changed.

ℹ️ Check
If the system is not a member of a domain, this is NA. If the firewall's Public Profile is not enabled (see V-17417), this requirement is also a finding. Verify the registry value below. If this registry value does not exist or is not configured as specified, this is a finding. Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \SOFTWARE\Policies\Microsoft\WindowsFirewall\PublicProfile\ Value Name: AllowLocalPolicyMerge Type: REG_DWORD Value: 0x00000000 (0)

ℹ️ Check

If the system is not a member of a domain, this is NA. If the firewall's Public Profile is not enabled (see V-17417), this requirement is also a finding. Verify the registry value below. If this registry value does not exist or is not configured as specified, this is a finding. Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \SOFTWARE\Policies\Microsoft\WindowsFirewall\PublicProfile\ Value Name: AllowLocalPolicyMerge Type: REG_DWORD Value: 0x00000000 (0)

✔️ Fix
If the system is not a member of a domain, this is NA. Configure the policy value for Computer Configuration >> Windows Settings >> Security Settings >> Windows Defender Firewall with Advanced Security >> Windows Defender Firewall with Advanced Security >> Windows Defender Firewall Properties (this link will be in the right pane) >> Public Profile tab >> Settings (select Customize) >> Rule merging, "Apply local firewall rules:" to "No".

✔️ Fix

If the system is not a member of a domain, this is NA. Configure the policy value for Computer Configuration >> Windows Settings >> Security Settings >> Windows Defender Firewall with Advanced Security >> Windows Defender Firewall with Advanced Security >> Windows Defender Firewall Properties (this link will be in the right pane) >> Public Profile tab >> Settings (select Customize) >> Rule merging, "Apply local firewall rules:" to "No".