CVE-2026-20860
📋 TL;DR
This vulnerability is a type confusion flaw in Windows Ancillary Function Driver for WinSock that allows an authenticated attacker to escalate privileges locally. It affects Windows systems with the vulnerable driver component. Attackers can gain SYSTEM-level privileges from a lower-privileged account.
💻 Affected Systems
- Windows Ancillary Function Driver for WinSock (afd.sys)
📦 What is this software?
Windows 10 1607 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 23h2 by Microsoft
Windows 11 24h2 by Microsoft
Windows 11 25h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with SYSTEM privileges, enabling installation of persistent malware, credential theft, and lateral movement across the network.
Likely Case
Local privilege escalation allowing attackers to bypass security controls, install additional malware, and access sensitive system resources.
If Mitigated
Limited impact if proper privilege separation and endpoint protection are in place, though successful exploitation still grants elevated access.
🎯 Exploit Status
Requires local access and authentication. Type confusion vulnerabilities typically require specific conditions to trigger reliably.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update Guide for specific KB numbers
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20860
Restart Required: Yes
Instructions:
1. Apply latest Windows security updates from Microsoft. 2. Restart affected systems. 3. Verify patch installation via Windows Update history.
🔧 Temporary Workarounds
Restrict local access
windowsLimit local login capabilities to trusted users only
Enable exploit protection
windowsConfigure Windows Defender Exploit Guard to mitigate privilege escalation attempts
🧯 If You Can't Patch
- Implement strict least privilege access controls to limit who can log in locally
- Deploy endpoint detection and response (EDR) solutions to monitor for privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check Windows version and build number, then compare against Microsoft's affected versions listCheck Version:
wmic os get caption, version, buildnumberVerify Fix Applied:
Verify Windows Update history shows the relevant security update installed📡 Detection & Monitoring
Log Indicators:
- Unusual process creation with SYSTEM privileges
- Suspicious driver loading events
- Security log events showing privilege escalation
Network Indicators:
- None - this is a local privilege escalation vulnerability
SIEM Query:
EventID=4688 AND NewProcessName contains 'cmd.exe' OR 'powershell.exe' AND SubjectUserName != SYSTEM AND TokenElevationType != %%1938