[REQ-END-085] ASR: Block executable files from running unless they meet a prevalence, age, or trusted list criterion

Target Scope

• Applicable Systems: Tier 2 client workstations and member servers.
• Operating Systems: Windows 10 (and above) Enterprise/Professional, Windows Server 2016 (and above).

Implementation Details

• Priority: High
• GPO Path / Registry Location:
  • GPO Path: Computer Configuration\Administrative Templates\Windows Components\Windows Defender Antivirus\Windows Defender Exploit Guard\Attack Surface Reduction
  • Registry Location:
    • HKLM\SOFTWARE\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules
      • 01443614-cd74-433a-b99e-2ecdc07bfc25 = 1 (REG_SZ)

Rationale

Blocks execution of unrecognized, newly compiled, or low-prevalence executable files. This provides initial protection against zero-day malware campaigns and targeted custom payloads that have not yet established reputation telemetry in the Microsoft Cloud Protection network.

Legacy Impact & Compatibility

Developers building and testing custom internal binaries, or administrators installing niche, uncertified third-party software updates will face false positives. Exclusions must be configured for target test directories.

Implementation Steps

Option A: Group Policy Object (GPO) Configuration (Preferred)

1. Navigate to: Computer Configuration\Administrative Templates\Windows Components\Windows Defender Antivirus\Windows Defender Exploit Guard\Attack Surface Reduction
2. Set 'Configure Attack Surface Reduction rules' to 'Enabled'
3. Click 'Show...' and add the rule GUID 01443614-cd74-433a-b99e-2ecdc07bfc25 as Value Name, with Value set to 1 (Block).

Option B: PowerShell & Registry Configuration (Remediation / Non-GPO)

Download Script: Configure-AsrLowPrevalence.ps1

# Configure-AsrLowPrevalence.ps1
$AsrRulesPath = "HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules"
if (-not (Test-Path $AsrRulesPath)) { New-Item -Path $AsrRulesPath -Force | Out-Null }
Set-ItemProperty -Path $AsrRulesPath -Name "01443614-cd74-433a-b99e-2ecdc07bfc25" -Value "1" -Type String -Force

To audit the hardening status: Download Script: Get-AsrLowPrevalenceStatus.ps1

# Get-AsrLowPrevalenceStatus.ps1
$AsrRulesPath = "HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender\Windows Defender Exploit Guard\ASR\Rules"
$Value = Get-ItemProperty -Path $AsrRulesPath -Name "01443614-cd74-433a-b99e-2ecdc07bfc25" -ErrorAction SilentlyContinue
if ($Value -and ($Value."01443614-cd74-433a-b99e-2ecdc07bfc25" -eq "1" -or $Value."01443614-cd74-433a-b99e-2ecdc07bfc25" -eq 1)) {
    Write-Output "Compliant"
    exit 0
} else {
    Write-Output "Non-Compliant"
    exit 1
}

Sources & Compliance References

• CIS Microsoft Windows 10 Benchmark: Section 18.9 (ASR rules config)
• ANSSI Active Directory Hardening Guide: Protective controls baselines on client workstations