Microsoft Defender AV must convert warn verdict to block.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-278677	SRG-APP-000210	WNDF-AV-000074	SV-278677r1144077_rule	2025-11-25	2

Description
If a site URL has an unknown or uncertain reputation, a toast notification presents the user with the following options: - Ok: The toast notification is released (removed), and the attempt to access the site is ended. - Unblock: The user has access to the site for 24 hours, at which point the block is reenabled. The user can continue to use Unblock to access the site until such time that the administrator prohibits (blocks) the site, thus removing the option to Unblock. - Feedback: The toast notification presents the user with a link to submit a ticket, which the user can use to submit feedback to the administrator in an attempt to justify access to the site.

Description

If a site URL has an unknown or uncertain reputation, a toast notification presents the user with the following options: - Ok: The toast notification is released (removed), and the attempt to access the site is ended. - Unblock: The user has access to the site for 24 hours, at which point the block is reenabled. The user can continue to use Unblock to access the site until such time that the administrator prohibits (blocks) the site, thus removing the option to Unblock. - Feedback: The toast notification presents the user with a link to submit a ticket, which the user can use to submit feedback to the administrator in an attempt to justify access to the site.

ℹ️ Check
Verify the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> Network Inspection System >> Convert warn verdict to block 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 "EnableConvertWarnToBlock" 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 >> Convert warn verdict to block 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 "EnableConvertWarnToBlock" 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 >> Convert warn verdict to block to "Enabled". Click "OK". Click "Apply".