CVE-2021-38638
📋 TL;DR
This vulnerability in Windows Ancillary Function Driver for WinSock allows attackers to escalate privileges from a low-privileged user account to SYSTEM level. It affects Windows systems where an attacker has local access. Successful exploitation requires an attacker to already have some level of access to the target system.
💻 Affected Systems
- Microsoft Windows
📦 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 7 by Microsoft
Windows 8.1 by Microsoft
Windows Rt 8.1 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with SYSTEM privileges, enabling installation of malware, data theft, lateral movement, and persistence mechanisms.
Likely Case
Local privilege escalation allowing attackers to bypass security controls, access sensitive data, and maintain persistence on compromised systems.
If Mitigated
Limited impact if proper access controls, least privilege principles, and network segmentation are implemented, though local compromise remains possible.
🎯 Exploit Status
Exploitation requires local access and low-privileged user credentials. Public proof-of-concept code exists.
🛠️ 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-2021-38638
Restart Required: Yes
Instructions:
1. Apply October 2021 Windows security updates via Windows Update. 2. For enterprise environments, deploy through WSUS or SCCM. 3. Restart affected systems after patch installation.
🔧 Temporary Workarounds
Restrict local access
windowsLimit local access to systems through strict access controls and least privilege principles.
Network segmentation
allSegment networks to limit lateral movement and contain potential privilege escalation.
🧯 If You Can't Patch
- Implement strict access controls and least privilege principles for all user accounts
- Monitor for suspicious privilege escalation attempts and implement enhanced logging
🔍 How to Verify
Check if Vulnerable:
Check Windows version and installed updates. Systems without October 2021 security updates are vulnerable.Check Version:
wmic os get caption, version, buildnumber, osarchitectureVerify Fix Applied:
Verify October 2021 security updates (KB5006670 for Windows 10 2004/20H2/21H1, KB5006674 for Windows 10 1909, etc.) are installed.📡 Detection & Monitoring
Log Indicators:
- Event ID 4688 with suspicious process creation, unexpected privilege escalation events, anomalous driver loading
Network Indicators:
- Unusual outbound connections from systems after local access
SIEM Query:
EventID=4688 AND (ProcessName="*\afd.sys*" OR CommandLine="*afd*")