Microsoft Defender AV must report Dynamic Signature dropped events.

Microsoft Defender Antivirus logs "Dynamic Signature dropped" events when it blocks or removes a file based on a dynamically updated signature, but the signature itself is dropped, meaning it was not fully processed or applied. This can indicate a potential issue with signature updates or the system's ability to handle them.

Verify the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> Reporting >> Configure whether to report Dynamic Signature dropped events 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\Reporting Criteria: If the value "EnableDynamicSignatureDroppedEventReporting" is REG_DWORD = 1, this is not a finding. If the value is 0, this is a finding.

Set the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> Reporting >> Configure whether to report Dynamic Signature dropped events to "Enabled".