CVE-2021-41367
📋 TL;DR
CVE-2021-41367 is an NTFS elevation of privilege vulnerability in Windows that allows authenticated attackers to gain SYSTEM-level privileges on affected systems. This affects Windows 10, Windows 11, and Windows Server systems with specific versions. Attackers need local access to exploit this vulnerability.
💻 Affected Systems
- Windows 10
- Windows 11
- Windows Server 2019
- Windows Server 2022
📦 What is this software?
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 10 by Microsoft
Windows 11 by Microsoft
Windows 11 by Microsoft
Windows 7 by Microsoft
Windows 8.1 by Microsoft
Windows Rt 8.1 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains full SYSTEM privileges, enabling complete system compromise, data theft, persistence establishment, and lateral movement across the network.
Likely Case
Privilege escalation from standard user to SYSTEM, allowing installation of malware, credential harvesting, and bypassing security controls.
If Mitigated
Limited impact with proper patch management, least privilege principles, and endpoint protection that can detect privilege escalation attempts.
🎯 Exploit Status
Exploit requires authenticated access but is relatively straightforward to execute once initial access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: October 2021 security updates (KB5006670, KB5006674, etc.)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-41367
Restart Required: Yes
Instructions:
1. Apply October 2021 Windows security updates through Windows Update. 2. For enterprise environments, deploy updates via WSUS, SCCM, or Intune. 3. Restart systems after patch installation.
🔧 Temporary Workarounds
Restrict local access
windowsLimit who has local login access to critical systems
Implement least privilege
windowsEnsure users operate with minimal necessary privileges
🧯 If You Can't Patch
- Implement application control policies to prevent unauthorized executables
- Deploy endpoint detection and response (EDR) solutions to detect privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check Windows version and compare with affected versions list. Vulnerable if running affected versions without October 2021 patches.Check Version:
winver or systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify October 2021 security updates are installed via 'wmic qfe list' or 'Get-Hotfix -Id KB5006670' (or relevant KB for your version).📡 Detection & Monitoring
Log Indicators:
- Event ID 4688 with parent process anomalies
- Unexpected SYSTEM privilege acquisition
- NTFS-related process creation with elevated privileges
Network Indicators:
- Lateral movement attempts following local privilege escalation
SIEM Query:
EventID=4688 AND (NewProcessName="*\system32\*" OR ParentProcessName="*\system32\*") AND SubjectUserName!="SYSTEM" AND TokenElevationType="%%1938"