CVE-2021-38628
📋 TL;DR
CVE-2021-38628 is an elevation of privilege vulnerability in the Windows Ancillary Function Driver for WinSock, allowing attackers to gain SYSTEM-level privileges on affected systems. It affects Windows operating systems and requires local access to exploit, potentially enabling full system compromise.
💻 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 7 by Microsoft
Windows 8.1 by Microsoft
Windows Rt 8.1 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
An attacker gains SYSTEM privileges, leading to complete system takeover, data theft, or deployment of persistent malware.
Likely Case
Local attackers escalate privileges to install programs, modify data, or create new accounts with administrative rights.
If Mitigated
With proper patching and least privilege controls, impact is limited to denial-of-service or minimal unauthorized access.
🎯 Exploit Status
Exploitation requires local access and low-level system interaction; public proof-of-concept code exists, increasing risk.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: October 2021 security updates or later; refer to Microsoft KB5006670 for details.
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-38628
Restart Required: Yes
Instructions:
1. Apply the October 2021 Windows security update via Windows Update or WSUS. 2. Restart the system to complete installation.
🔧 Temporary Workarounds
Disable vulnerable driver
windowsTemporarily disable the Ancillary Function Driver to reduce attack surface; may impact some networking features.
sc config afd start= disabled
sc stop afd
🧯 If You Can't Patch
- Implement strict access controls and least privilege principles to limit local user capabilities.
- Monitor for suspicious activity and use application whitelisting to prevent unauthorized execution.
🔍 How to Verify
Check if Vulnerable:
Check if the system has the October 2021 security update installed; if not, it is likely vulnerable.Check Version:
wmic os get versionVerify Fix Applied:
Verify that the system version matches or exceeds the patched version from the Microsoft advisory.📡 Detection & Monitoring
Log Indicators:
- Unusual process creation with SYSTEM privileges, especially from non-admin users.
- Driver-related errors or crashes in system logs.
Network Indicators:
- Not applicable; this is a local privilege escalation vulnerability.
SIEM Query:
Example: EventID 4688 with elevated privileges from suspicious parent processes.