Microsoft Defender AV must be configured to block executable content from email client and webmail.

Documentable No

Rule ID SV-213456r961092_rule

CCI References

CCI-001170

Discussion

This rule blocks the following file types from being run or launched from an email seen in either Microsoft Outlook or webmail (such as Gmail.com or Outlook.com): Executable files (such as .exe, .dll, or .scr) Script files (such as a PowerShell .ps, VisualBasic .vbs, or JavaScript .js file) Script archive files

Check Procedure

This setting is applicable starting with v1709 of Windows 10. It is NA for prior versions.

Verify the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> Microsoft Defender Exploit Guard >> Attack Surface Reduction >> "Configure Attack Surface Reduction rules" is set to "Enabled”.  Click "Show...". Verify the rule ID in the Value name column and the desired state in the Value column is set as follows:
Value name: BE9BA2D9-53EA-4CDC-84E5-9B1EEEE46550
Value:  1

Procedure: Use the Windows Registry Editor to navigate to the following key: 
HKLM\Software\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules

Criteria: If the value "BE9BA2D9-53EA-4CDC-84E5-9B1EEEE46550" is REG_SZ = 1, this is not a finding.

Fix Action

Set the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Microsoft Defender Antivirus >> Windows Defender Exploit Guard >> Attack Surface Reduction >> "Configure Attack Surface Reduction rules" to "Enabled". 

Click "Show...". Set the Value name to "BE9BA2D9-53EA-4CDC-84E5-9B1EEEE46550" and the Value to "1".