Microsoft Defender AV must enable asynchronous inspection.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-278678	SRG-APP-000210	WNDF-AV-000075	SV-278678r1144079_rule	2025-11-25	2

Description
Network protection includes performance optimization that allows block mode to asynchronously inspect long-lived connections, which might provide a performance improvement. This optimization can also help with app compatibility problems.

ℹ️ Check
Verify the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> Network Inspection System >> Turn on asynchronous inspection is set to "Enabled"; otherwise, this is a finding. Procedure: Use the Windows Registry Editor to navigate to the following key: HKLM\Software\Policies\Microsoft\Windows Defender\NIS Criteria: If the value "AllowSwitchToAsyncInspection" is REG_DWORD = 1, this is not a finding. If the value is 0, this is a finding.

ℹ️ Check

Verify the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> Network Inspection System >> Turn on asynchronous inspection is set to "Enabled"; otherwise, this is a finding. Procedure: Use the Windows Registry Editor to navigate to the following key: HKLM\Software\Policies\Microsoft\Windows Defender\NIS Criteria: If the value "AllowSwitchToAsyncInspection" is REG_DWORD = 1, this is not a finding. If the value is 0, this is a finding.

✔️ Fix
Set the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> MpEngine >> Turn on asynchronous inspection to "Enabled". Click "OK". Click "Apply".