The Windows Defender SmartScreen for Explorer must be enabled.

Windows Defender SmartScreen helps protect systems from programs downloaded from the internet that may be malicious. Enabling Windows Defender SmartScreen will warn or prevent users from running potentially malicious programs.

This is applicable to unclassified systems, for other systems this is NA.

If the following registry values do not exist or are not configured as specified, this is a finding:

Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \SOFTWARE\Policies\Microsoft\Windows\System\

Value Name: EnableSmartScreen

Value Type: REG_DWORD Value: 0x00000001 (1)

And

Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \SOFTWARE\Policies\Microsoft\Windows\System\

Value Name: ShellSmartScreenLevel

Value Type: REG_SZ Value: Block

v1607 LTSB:

Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \SOFTWARE\Policies\Microsoft\Windows\System\

Value Name: EnableSmartScreen

Value Type: REG_DWORD Value: 0x00000001 (1)

v1507 LTSB:

Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \SOFTWARE\Policies\Microsoft\Windows\System\

Value Name: EnableSmartScreen

Value Type: REG_DWORD Value: 0x00000002 (2)

Configure the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> File Explorer >> "Configure Windows Defender SmartScreen" to "Enabled" with "Warn and prevent bypass" selected.

Windows 10 includes duplicate policies for this setting. It can also be configured under Computer Configuration >> Administrative Templates >> Windows Components >> Windows Defender SmartScreen >> Explorer.

v1607 LTSB: Configure the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> File Explorer >> "Configure Windows SmartScreen" to "Enabled". (Selection options are not available.)

v1507 LTSB: Configure the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> File Explorer >> "Configure Windows SmartScreen" to "Enabled" with "Require approval from an administrator before running downloaded unknown software" selected.