CVE-2022-24521: Windows 10 Privilege Escalation Vulnerability

CVE-2022-24521 Overview

CVE-2022-24521 is an elevation of privilege vulnerability in the Windows Common Log File System (CLFS) driver. The flaw allows a local, authenticated attacker to execute code with SYSTEM privileges on affected Windows systems. Microsoft published the advisory on April 12, 2022, and CISA added the CVE to its Known Exploited Vulnerabilities (KEV) catalog the same week after confirming in-the-wild exploitation. The vulnerability affects every supported Windows client and server release at the time of disclosure, from Windows 7 SP1 through Windows 11 21H2 and Windows Server 2022. The underlying weakness is tracked as an out-of-bounds write [CWE-787] inside the CLFS.sys kernel driver.

Critical Impact

A local attacker with low-privileged access can elevate to SYSTEM, enabling full host compromise. CISA KEV listing confirms active exploitation, and the EPSS score of 8.362% places it in the 92nd percentile for likelihood of exploitation.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 1909, 20H2, 21H1, 21H2) and Windows 11 21H2
• Microsoft Windows 7 SP1, Windows 8.1, and Windows RT 8.1
• Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, and Server 20H2

Discovery Timeline

• 2022-04-15 - CVE-2022-24521 published to the National Vulnerability Database
• 2025-10-30 - Last updated in NVD database

Technical Details for CVE-2022-24521

Vulnerability Analysis

The vulnerability resides in the Common Log File System driver (CLFS.sys), a kernel-mode component that provides high-performance, general-purpose log file services to user-mode and kernel-mode clients. CLFS has historically been a fertile target for privilege escalation research because it parses complex on-disk log structures (Base Log Files, or BLFs) inside the kernel. CVE-2022-24521 is classified as an out-of-bounds write [CWE-787], meaning the driver writes data past the bounds of an allocated kernel buffer. The bug is reachable from any local context that can interact with CLFS APIs, including standard user sessions and sandboxed processes that retain access to the CLFS device.

Root Cause

The root cause is improper validation of fields within attacker-controlled CLFS log structures before they are used to compute write offsets inside kernel memory. By crafting a malformed BLF, an attacker influences pointer arithmetic in CLFS parsing routines, producing a write to a kernel address chosen by the attacker. Out-of-bounds writes inside CLFS.sys corrupt adjacent kernel objects, which an attacker can leverage to overwrite security tokens or function pointers and gain SYSTEM execution.

Attack Vector

Exploitation requires local access and low privileges, with no user interaction. A typical attack chain begins with initial access through phishing, a malicious document, or commodity malware running as a standard user. The attacker then opens a handle to the CLFS device, submits a crafted log file or log operation, and triggers the out-of-bounds write. Successful exploitation replaces the access token of the attacker's process with the SYSTEM token, enabling installation of persistent implants, disabling of security tooling, and lateral movement.

No public proof-of-concept is referenced in the NVD record, but Microsoft and CISA have confirmed the vulnerability is being exploited in the wild. Technical details of the kernel parsing flaw are documented in the Microsoft Security Update Guide for CVE-2022-24521.

Detection Methods for CVE-2022-24521

Indicators of Compromise

• Unexpected creation of Base Log Files (.blf) or container files in non-standard directories outside %SystemRoot%\System32\config\ and user profile log paths.
• Standard-user processes spawning child processes running as NT AUTHORITY\SYSTEM without a legitimate service or scheduled task parent.
• Crash dumps or bug-check events referencing CLFS.sys on hosts that previously had no CLFS instability.

Detection Strategies

• Hunt for token manipulation patterns where a process owned by a low-privileged user suddenly executes with SYSTEM integrity, a common post-exploitation signal for kernel EoP bugs.
• Monitor for kernel-mode driver loads or modifications around the time of suspicious CLFS activity, which can indicate follow-on rootkit installation.
• Correlate CLFS API misuse with subsequent credential dumping tools such as those targeting LSASS, which frequently follow successful elevation.

Monitoring Recommendations

• Enable and forward Windows Security event IDs 4688 (process creation) and 4672 (special privileges assigned) to a centralized analytics platform for behavioral analysis.
• Track Microsoft-Windows-Kernel-General and CLFS ETW providers for anomalous log file creation patterns originating from user-writable directories.
• Maintain an inventory of patched versus unpatched endpoints and prioritize monitoring on systems that cannot be immediately updated.

How to Mitigate CVE-2022-24521

Immediate Actions Required

• Apply the Microsoft April 2022 security updates to all affected Windows clients and servers without delay; this CVE is listed in the CISA KEV catalog and is subject to federal remediation deadlines.
• Identify legacy systems (Windows 7, Windows 8.1, Server 2008/2012) and ensure Extended Security Updates are installed where applicable.
• Audit privileged service accounts and reset credentials on any host suspected of post-exploitation activity.

Patch Information

Microsoft released fixes for CVE-2022-24521 as part of the April 12, 2022 Patch Tuesday rollup. Administrators should consult the Microsoft Security Update Guide for CVE-2022-24521 to identify the correct KB article for each Windows build. The vulnerability is also tracked in the CISA Known Exploited Vulnerabilities Catalog, which mandates remediation for U.S. federal agencies.

Workarounds

• No official workaround replaces patching; reduce risk by restricting interactive logon and limiting local user privileges on high-value hosts.
• Enforce application allowlisting (Windows Defender Application Control or AppLocker) to block unauthorized binaries that would stage CLFS exploitation.
• Segment legacy or unpatchable systems behind jump hosts and disable non-essential local accounts to reduce the local attack surface.

# Verify the CLFS driver version on a Windows host (PowerShell)
Get-Item C:\Windows\System32\drivers\CLFS.sys | Select-Object Name, VersionInfo

# Confirm the April 2022 cumulative update is installed
Get-HotFix | Where-Object { $_.InstalledOn -ge (Get-Date '2022-04-12') } |
    Sort-Object InstalledOn -Descending