SV-213461r961092: Microsoft Defender AV must be configured to block execution of potentially obfuscated scripts. | Microsoft Defender Antivirus STIG SCAP Benchmark

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Assessment Title

Rule Text

Microsoft Defender AV must be configured to block execution of potentially obfuscated scripts.

Description

Discussion Text

Malware and other threats can attempt to obfuscate or hide their malicious code in some script files. This rule prevents scripts that appear to be obfuscated from running. It uses the AntiMalwareScanInterface (AMSI) to determine if a script is potentially obfuscated and then blocks such a script or blocks scripts when an attempt is made to access them.

How this relates to the STIG checklist: STIG vs SCAP benchmark.

IA Controls

NIST SP 800-53

Not mappedCCI-001170SV-92671V-77975

References

DPMS Target Microsoft Defender Antivirus DISA DPMS Target Microsoft Defender Antivirus 3985

SCC Automation Reference

The reconstructed evaluation script behind this rule's OVAL check(s) — every module a compound check combines, with this rule's own concrete values and DISA's SCC tool's real per-module mechanism curated from static teardown of SCC releases.

# Windows PowerShell
# Reconstructed from oval:mil.disa.stig.defenderantivirus:def:36
# Microsoft Defender AV must be configured to block execution of potentially obfuscated scripts.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# Verify Windows 10 is release id 1709 or newer
# registry_object (registry_test)
function test_1 {
  return (((@{String='reg_sz';ExpandString='reg_expand_sz';Binary='reg_binary';DWord='reg_dword';MultiString='reg_multi_sz';QWord='reg_qword';None='reg_none'}[(Get-Item -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion').GetValueKind('ReleaseId').ToString()]) -eq 'reg_sz') -and (((Get-ItemProperty -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion' -Name 'ReleaseId' -ErrorAction SilentlyContinue) | Select-Object -ExpandProperty 'ReleaseId') -ge '1709'))
}
# Computer Configuration\Administrative Templates\Windows Components\Microsoft Defender Antivirus\Microsoft Defender Exploit Guard\Attack Surface Reduction\Configure Attack Surface Reduction rules4CC
# registry_object (registry_test)
function test_2 {
  return (((@{String='reg_sz';ExpandString='reg_expand_sz';Binary='reg_binary';DWord='reg_dword';MultiString='reg_multi_sz';QWord='reg_qword';None='reg_none'}[(Get-Item -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules').GetValueKind('5BEB7EFE-FD9A-4556-801D-275E5FFC04CC').ToString()]) -eq 'reg_sz') -and (((Get-ItemProperty -Path 'Registry::HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules' -Name '5BEB7EFE-FD9A-4556-801D-275E5FFC04CC' -ErrorAction SilentlyContinue) | Select-Object -ExpandProperty '5BEB7EFE-FD9A-4556-801D-275E5FFC04CC') -eq '1'))
}

if ((test_1 -or test_2)) {
  Write-Output "PASS"
} else {
  Write-Output "FAIL"
}

Assessment Script Powered by AISyntax-verified

A standalone PowerShell script to assess this control automatically. Review before running it in your environment.

Syntax-checked as valid PowerShell. Not executed here — running it for real needs the actual ms_defender_antivirus target this check assesses.

# OVAL Definition: oval:mil.disa.stig.defenderantivirus:def:36
$releaseVersion = (Get-ItemProperty -Path "HKLM:\Software\Microsoft\Windows NT\CurrentVersion").ReleaseId
if ($releaseVersion -ge 1709 -or (Test-Path -Path "HKLM:\Software\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules\5BEB7EFE-FD9A-4556-801D-275E5FFC04CC" -and (Get-ItemProperty -Path "HKLM:\Software\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules\5BEB7EFE-FD9A-4556-801D-275E5FFC04CC").Value -eq "1")) { Write-Output "PASS"; Exit 0 } else { Write-Output "FAIL"; Exit 1 }

Remediation

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 "5BEB7EFE-FD9A-4556-801D-275E5FFC04CC" and the Value to "1".