CVE-2023-35299
📋 TL;DR
This vulnerability in the Windows Common Log File System (CLFS) driver allows an authenticated attacker to gain SYSTEM-level privileges through a local exploit. It affects Windows systems where an attacker already has some level of access. The vulnerability stems from improper bounds checking in the CLFS driver.
💻 Affected Systems
- Windows 10
- Windows 11
- Windows Server 2016
- Windows Server 2019
- Windows Server 2022
📦 What is this software?
Windows 10 1507 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 21h2 by Microsoft
Windows 11 22h2 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
Local privilege escalation from a standard user account to SYSTEM, allowing installation of malware, disabling security controls, and accessing sensitive data.
If Mitigated
Limited impact if proper privilege separation exists and users operate with minimal privileges, though SYSTEM access remains possible if exploited.
🎯 Exploit Status
Exploitation requires local access and some technical knowledge. Proof-of-concept code has been published, making weaponization likely.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: July 2023 security updates (KB5028166 for Windows 10 21H2, KB5028185 for Windows 11 22H2, etc.)
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-35299
Restart Required: Yes
Instructions:
1. Apply the July 2023 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
windowsLimit local user access to systems through strict access controls and privilege management.
🧯 If You Can't Patch
- Implement strict least privilege principles to limit damage from successful exploitation
- Monitor for suspicious privilege escalation attempts using security tools
🔍 How to Verify
Check if Vulnerable:
Check if July 2023 security updates are installed via 'winver' or 'systeminfo' command.Check Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify that KB5028166 (or relevant July 2023 KB) is listed in installed updates in Windows Update history.📡 Detection & Monitoring
Log Indicators:
- Event ID 4688 with privileged process creation from non-privileged users
- Unexpected SYSTEM privilege acquisition
Network Indicators:
- None - this is a local exploit
SIEM Query:
EventID=4688 AND NewProcessName="*" AND SubjectUserName!="SYSTEM" AND TokenElevationType="%%1938"