Microsoft Office Security Feature Bypass Vulnerability (CVE-2026-21509) Analysis and Mitigation Guide

# Force Microsoft Office Click-to-Run client to check and apply the latest security updates
Start-Process -FilePath 'C:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeC2RClient.exe' -ArgumentList '/update user updatetoversion=16.0.xxxxx.xxxxx' -Wait -NoNewWindow

# Block macros from running in Office files from the Internet via Registry
$RegPath = 'HKCU:\Software\Policies\Microsoft\Office\16.0\common\security'
if (-not (Test-Path $RegPath)) { New-Item -Path $RegPath -Force }
New-ItemProperty -Path $RegPath -Name 'blockcontentexecutionfrominternet' -Value 1 -PropertyType DWord -Force

# Enforce Protected View for email attachments
New-ItemProperty -Path $RegPath -Name 'disableprotectedviewforattachments' -Value 0 -PropertyType DWord -Force

# Audit script to check Microsoft Office version and vulnerability exposure
$OfficePath = 'HKLM:\SOFTWARE\Microsoft\Office\ClickToRun\Configuration'
if (Test-Path $OfficePath) {
    $Version = (Get-ItemProperty -Path $OfficePath).ClientVersionToReport
    Write-Host 'Current Installed Microsoft Office Version:' $Version
    # Replace with the actual patched version threshold
    if ([Version]$Version -lt [Version]'16.0.15000.20000') {
        Write-Warning 'Warning: The system is likely vulnerable to CVE-2026-21509. Immediate patching is required.'
    } else {
        Write-Host 'Security Status: Office is updated to a secure version.' -ForegroundColor Green
    }
} else {
    Write-Host 'Microsoft Office ClickToRun configuration not found.'
}