CVE-2021-43238
📋 TL;DR
This vulnerability allows an authenticated attacker to execute code with SYSTEM privileges on Windows systems by exploiting improper link resolution in Remote Access components. It affects Windows 10, Windows 11, and Windows Server systems with Remote Access enabled. Attackers need local access to the target system to exploit this flaw.
💻 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 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 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 10 by Microsoft
Windows 11 by Microsoft
Windows 11 by Microsoft
Windows 7 by Microsoft
Windows 7 by Microsoft
Windows 8.1 by Microsoft
Windows 8.1 by Microsoft
Windows Rt 8.1 by Microsoft
Windows Server by Microsoft
Windows Server by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with SYSTEM privileges, enabling complete control over the affected system, data theft, lateral movement, and persistence establishment.
Likely Case
Privilege escalation from a standard user account to SYSTEM privileges, allowing installation of malware, credential harvesting, and bypassing security controls.
If Mitigated
Limited impact with proper network segmentation, least privilege enforcement, and endpoint protection that detects privilege escalation attempts.
🎯 Exploit Status
Exploit requires authenticated access but is relatively straightforward to execute once access is obtained. Proof-of-concept code has been published.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: January 2022 security updates (KB5009543 for Windows 10 20H2, KB5009566 for Windows 11, etc.)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43238
Restart Required: Yes
Instructions:
1. Apply January 2022 Windows security updates via Windows Update. 2. For enterprise environments, deploy updates through WSUS or SCCM. 3. Restart systems after patch installation.
🔧 Temporary Workarounds
Disable Remote Access Service
windowsTemporarily disable the Remote Access service if not required for business operations
sc config RemoteAccess start= disabled
net stop RemoteAccess
Restrict Access to Vulnerable Components
windowsUse Windows Firewall to block unnecessary access to Remote Access components
netsh advfirewall firewall add rule name="Block RemoteAccess" dir=in action=block program="%SystemRoot%\System32\svchost.exe" service=RemoteAccess
🧯 If You Can't Patch
- Implement strict least privilege access controls to limit who can authenticate to vulnerable systems
- Deploy endpoint detection and response (EDR) solutions to monitor for privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check if Remote Access service is running and system has unpatched January 2022 updates: sc query RemoteAccess | findstr RUNNINGCheck Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify January 2022 security updates are installed: wmic qfe list | findstr KB5009543 (or appropriate KB for your version)📡 Detection & Monitoring
Log Indicators:
- Event ID 4688 with parent process svchost.exe and RemoteAccess service
- Unexpected privilege escalation events in Security logs
- Process creation from RemoteAccess service context
Network Indicators:
- Unusual outbound connections from systems with RemoteAccess enabled
- Lateral movement attempts from recently compromised systems
SIEM Query:
source="windows_security" EventCode=4688 ParentProcessName="svchost.exe" NewProcessName="cmd.exe" OR NewProcessName="powershell.exe" | where ProcessCommandLine contains "RemoteAccess"