CVE-2025-21418
📋 TL;DR
This vulnerability in Windows Ancillary Function Driver for WinSock allows attackers to gain SYSTEM-level privileges by exploiting a heap-based buffer overflow. It affects Windows systems with the vulnerable driver component. Attackers need local access to exploit this vulnerability.
💻 Affected Systems
- Microsoft Windows
📦 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 22h2 by Microsoft
Windows 11 23h2 by Microsoft
Windows 11 24h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with SYSTEM privileges, enabling installation of malware, data theft, and persistence mechanisms.
Likely Case
Privilege escalation from standard user to SYSTEM, allowing attackers to bypass security controls and execute arbitrary code.
If Mitigated
Limited impact due to proper access controls, but still enables privilege escalation within the compromised account's scope.
🎯 Exploit Status
Requires local access and user privileges. Exploitation involves triggering a heap-based buffer overflow in the AFD driver.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: February 2025 security updates (KB5034765 for Windows 10, KB5034766 for Windows 11, etc.)
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21418
Restart Required: Yes
Instructions:
1. Apply February 2025 Windows security updates via Windows Update. 2. For enterprise environments, deploy updates through WSUS or Microsoft Endpoint Configuration Manager. 3. Restart systems after patch installation.
🔧 Temporary Workarounds
Restrict local access
allLimit physical and remote access to vulnerable systems to trusted users only.
Enable Windows Defender Exploit Guard
allConfigure Exploit Guard to mitigate exploitation techniques.
🧯 If You Can't Patch
- Implement strict access controls and least privilege principles
- Monitor for suspicious privilege escalation attempts and driver-related activities
🔍 How to Verify
Check if Vulnerable:
Check if afd.sys driver version is vulnerable by comparing to patched versions in Microsoft advisory.Check Version:
wmic datafile where name='C:\\Windows\\System32\\drivers\\afd.sys' get versionVerify Fix Applied:
Verify February 2025 security updates are installed and afd.sys driver version matches patched version.📡 Detection & Monitoring
Log Indicators:
- Unusual privilege escalation events
- Suspicious driver loading or modification
- Process creation with SYSTEM privileges from user accounts
Network Indicators:
- Not applicable - local exploitation only
SIEM Query:
EventID=4688 AND NewProcessName contains 'cmd.exe' OR 'powershell.exe' AND SubjectUserName != SYSTEM AND TokenElevationType != %%1936