CVE-2026-20804
📋 TL;DR
This Windows Hello vulnerability allows an unauthorized local attacker to tamper with authentication processes due to incorrect privilege assignment. It affects Windows systems using Windows Hello for biometric or PIN authentication. Attackers must have physical or remote desktop access to exploit this.
💻 Affected Systems
- Windows Hello
📦 What is this software?
Windows 10 1607 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 23h2 by Microsoft
Windows 11 24h2 by Microsoft
Windows 11 25h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Attacker could bypass Windows Hello authentication entirely, gain unauthorized system access, or manipulate biometric/PIN data to impersonate legitimate users.
Likely Case
Local privilege escalation allowing attackers to modify Windows Hello configurations or bypass certain authentication checks while maintaining some system access requirements.
If Mitigated
With proper access controls and monitoring, impact is limited to isolated systems where attackers already have some local access.
🎯 Exploit Status
Requires local access and knowledge of Windows Hello internals. No public exploit code available at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update Guide for specific KB numbers
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20804
Restart Required: Yes
Instructions:
1. Open Windows Update Settings 2. Check for updates 3. Install all security updates 4. Restart system when prompted
🔧 Temporary Workarounds
Disable Windows Hello
windowsTemporarily disable Windows Hello biometric and PIN authentication
gpedit.msc > Computer Configuration > Administrative Templates > Windows Components > Windows Hello for Business > Set to Disabled
Require Additional Authentication Factor
windowsConfigure Windows Hello to require password in addition to biometric/PIN
secpol.msc > Local Policies > Security Options > Interactive logon: Require Windows Hello for Business or smart card > Set to Enabled
🧯 If You Can't Patch
- Implement strict physical access controls to prevent unauthorized local access
- Enable enhanced auditing for Windows Hello events and monitor for suspicious authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check Windows version and verify Windows Hello is enabled in Settings > Accounts > Sign-in optionsCheck Version:
winverVerify Fix Applied:
Verify latest Windows updates are installed via winver command and check Windows Hello functionality📡 Detection & Monitoring
Log Indicators:
- Windows Security event logs with Event ID 4625 (failed logon) followed by successful Windows Hello authentication
- Unexpected modifications to Windows Hello registry keys or configuration files
Network Indicators:
- N/A - local exploitation only
SIEM Query:
EventID=4625 AND AuthenticationPackageName="Windows Hello" | stats count by TargetUserName