Ensure 'Configure the 'Block at First Sight' feature' is set to 'Enabled'

HighLevel 1Automateddefender

Description

This policy setting configures whether the device checks (in real time) with the Microsoft Active Protection Service (MAPS) before allowing certain content to be run or accessed. The block at first sight feature works when Microsoft Defender Antivirus encounters a suspicious but undetected file. Rationale: Enabling the Block at First Sight feature enhances threat protection by using next-generation protection to detect new malware and block it within seconds. Audit reads the Group Policy registry value and prints 'compliant', 'unset' (policy not configured, reported as FAIL) or the non-compliant value. Registry value: HKLM\SOFTWARE\Policies\Microsoft\Windows Defender\Spynet:DisableBlockAtFirstSeen (REG_DWORD); compliant when it is 0. Remediation writes 0 locally; in a domain set it through the ADMX so Group Policy does not revert it.

How it is checked

Audit method: Windows registry

registry

$v = (Get-ItemProperty -Path 'Registry::HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Spynet' -Name 'DisableBlockAtFirstSeen' -ErrorAction SilentlyContinue).'DisableBlockAtFirstSeen'; if ($null -eq $v) { 'unset' } elseif (($null -ne $v -and @(0) -contains [int64]$v)) { 'compliant' } else { "non-compliant: $v" }

Expected output: compliant

How it is fixed

Fix method: Shell command

shell

$p = 'Registry::HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Spynet'; if (-not (Test-Path -Path $p)) { New-Item -Path $p -Force | Out-Null }; New-ItemProperty -Path $p -Name 'DisableBlockAtFirstSeen' -Value 0 -PropertyType DWord -Force | Out-Null

Properties

Operating systems: Any
Tags: defenderantiviruscis-l1
Reference: CIS Microsoft Defender Antivirus Benchmark v1.0.0 - 1.5.2 Ensure 'Configure the 'Block at First Sight' feature' is set to 'Enabled'

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target defender