CVE-2022-35803: Windows 10 Privilege Escalation Vulnerability

CVE-2022-35803 Overview

CVE-2022-35803 is an elevation of privilege vulnerability in the Windows Common Log File System (CLFS) Driver that affects a wide range of Microsoft Windows operating systems. The CLFS driver is a kernel-mode component responsible for managing high-performance transaction logs used by various Windows services and applications. A local attacker who successfully exploits this vulnerability could gain elevated privileges on the affected system, potentially achieving SYSTEM-level access.

Critical Impact

Successful exploitation allows a low-privileged local attacker to escalate privileges to SYSTEM level, enabling complete control over the affected Windows system including the ability to install programs, view/change/delete data, or create new accounts with full user rights.

Affected Products

• Microsoft Windows 10 (multiple versions including 1607, 1809, 20H2, 21H1, 21H2)
• Microsoft Windows 11 (ARM64 and x64)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022 (including Azure editions)

Discovery Timeline

• 2022-09-13 - CVE-2022-35803 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-35803

Vulnerability Analysis

The Windows Common Log File System (CLFS) driver (clfs.sys) is a critical kernel-mode component that provides a general-purpose logging infrastructure used by numerous Windows subsystems and applications. This elevation of privilege vulnerability exists due to improper handling of objects in memory within the CLFS driver.

The vulnerability requires local access and low privileges to exploit, meaning an attacker must first gain the ability to execute code on the target system. However, no user interaction is required for exploitation. Once exploited, the attacker can achieve complete compromise of system confidentiality, integrity, and availability.

CLFS vulnerabilities are particularly concerning because they operate at the kernel level, and successful exploitation typically results in code execution with SYSTEM privileges—the highest level of access on a Windows system.

Root Cause

The vulnerability stems from improper memory handling within the CLFS driver. While Microsoft has not disclosed specific technical details about the root cause (classified as NVD-CWE-noinfo), CLFS vulnerabilities historically involve issues such as improper validation of Base Log File (BLF) structures, type confusion errors, or out-of-bounds memory access when processing log file metadata.

The CLFS driver processes specialized log file formats that contain complex data structures. Improper validation or handling of these structures can lead to memory corruption conditions that attackers can leverage to achieve privilege escalation.

Attack Vector

This vulnerability requires local access to the target system, meaning an attacker must first establish a foothold through another means such as phishing, exploitation of a different vulnerability, or through legitimate but limited access.

The attack flow typically involves:

1. An attacker with low-privilege local access creates or manipulates a malformed CLFS log file
2. The attacker triggers the CLFS driver to process the crafted file
3. The driver improperly handles the malicious input, causing memory corruption
4. The attacker leverages this corruption to execute arbitrary code with SYSTEM privileges

This type of vulnerability is commonly used in attack chains where initial access has already been obtained, and the attacker needs to escalate privileges for lateral movement or persistence.

Detection Methods for CVE-2022-35803

Indicators of Compromise

• Unusual access to or creation of .blf (Base Log File) files in unexpected directories
• Suspicious processes spawning with elevated privileges from low-privilege parent processes
• Abnormal activity involving the clfs.sys driver or CLFS-related API calls
• Unexpected SYSTEM-level process creation following user-initiated actions

Detection Strategies

• Monitor for attempts to load or manipulate BLF files from non-standard locations using Windows Event Logging
• Implement behavioral detection rules for privilege escalation patterns targeting kernel drivers
• Enable Windows Defender Exploit Guard and Attack Surface Reduction (ASR) rules to detect exploitation attempts
• Deploy endpoint detection and response (EDR) solutions capable of detecting kernel-level anomalies

Monitoring Recommendations

• Enable detailed logging for process creation events (Event ID 4688) with command-line auditing
• Monitor for suspicious driver loading activity and unexpected kernel-mode code execution
• Implement file integrity monitoring on critical system directories where CLFS log files may be stored
• Correlate low-privilege user activity with subsequent elevated privilege process creation

How to Mitigate CVE-2022-35803

Immediate Actions Required

• Apply the Microsoft security update from the September 2022 Patch Tuesday release immediately
• Prioritize patching on systems where local users have interactive access
• Review and restrict local access privileges following the principle of least privilege
• Ensure endpoint protection solutions are updated with the latest detection signatures

Patch Information

Microsoft addressed this vulnerability in the September 2022 security updates. Organizations should apply the appropriate update for their Windows version as listed in the Microsoft CVE-2022-35803 Advisory. The security update corrects how the CLFS driver handles objects in memory, eliminating the vulnerability.

For systems that cannot be immediately patched, administrators should implement additional monitoring and access controls while planning for deployment of the security update.

Workarounds

• Restrict local logon rights to only necessary users on sensitive systems using Group Policy
• Implement application whitelisting to prevent unauthorized code execution
• Enable Credential Guard and other Windows security features to limit the impact of privilege escalation
• Consider network segmentation to isolate systems that cannot be immediately patched

# PowerShell: Check if the security update is installed
Get-HotFix | Where-Object {$_.InstalledOn -ge "2022-09-13"} | Select-Object HotFixID, InstalledOn

# PowerShell: Audit local user privileges
Get-LocalGroupMember -Group "Administrators"
Get-LocalGroupMember -Group "Users"