CVE-2021-41370
📋 TL;DR
This vulnerability allows an authenticated attacker to gain SYSTEM-level privileges on Windows systems by exploiting a flaw in NTFS file system handling. It affects Windows servers and workstations where an attacker has local access. Successful exploitation requires the attacker to already have some level of access to the system.
💻 Affected Systems
- Windows 10
- Windows 11
- Windows Server 2016
- 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 or service account to SYSTEM, allowing installation of malware, credential harvesting, and bypassing security controls.
If Mitigated
Limited impact due to proper access controls, least privilege principles, and network segmentation preventing lateral movement.
🎯 Exploit Status
Exploit requires authenticated access but is relatively straightforward to execute once access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: October 2021 security updates (KB5006670, KB5006672, etc.)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-41370
Restart Required: Yes
Instructions:
1. Apply October 2021 Windows security updates from Windows Update. 2. For enterprise environments, deploy through WSUS or SCCM. 3. Restart systems after patch installation.
🔧 Temporary Workarounds
Restrict user permissions
windowsImplement least privilege principles to limit what authenticated users can do on systems
Network segmentation
allSegment critical systems to limit lateral movement if privilege escalation occurs
🧯 If You Can't Patch
- Implement strict access controls and monitor for privilege escalation attempts
- Deploy application whitelisting to prevent execution of unauthorized binaries
🔍 How to Verify
Check if Vulnerable:
Check Windows Update history for October 2021 security updates or run 'systeminfo' command and verify build number is after the patched versionsCheck Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify October 2021 security updates are installed via Windows Update history or check build number matches patched versions📡 Detection & Monitoring
Log Indicators:
- Windows Security Event ID 4688 (process creation) showing unexpected SYSTEM privilege processes
- Event ID 4672 (special privileges assigned) for unusual accounts
Network Indicators:
- Unusual outbound connections from previously low-privilege accounts
- Lateral movement attempts from compromised systems
SIEM Query:
EventID=4688 AND NewProcessName="*" AND SubjectUserName!="SYSTEM" AND TokenElevationType="%%1938"