Windows Common Log File System (CLFS) Driver Use-After-Free Local Privilege Escalation Vulnerability (CVE-2025-29824) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTWindows 10, Windows 11, and Windows Server operating systems utilizing the Common Log File System (CLFS.sys) driver.
An authorized local attacker can execute arbitrary code in kernel mode and elevate privileges to NT AUTHORITY\SYSTEM.
Immediately apply the latest cumulative security updates released by Microsoft (March 2025 Patch Tuesday or later).
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
The primary remediation is to apply the official Microsoft cumulative updates. You can force the update process via PowerShell on managed endpoints.
# Install and import the PSWindowsUpdate module to force cumulative updates
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck
Get-WindowsUpdate -AcceptAll -Install -AutoReboot2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict local access, monitor suspicious process creation, and restrict write permissions on public directories where malicious .blf files might be dropped.
# Enable advanced auditing for process creation to monitor suspicious child processes
auditpol /set /subcategory:'Process Creation' /success:enable /failure:enable
# Restrict write/create file permissions for non-admin users in public directories (Example)
$Path = 'C:\Users\Public\Documents'
$Acl = Get-Acl $Path
$Ar = New-Object System.Security.AccessControl.FileSystemAccessRule('Everyone', 'CreateFiles', 'Deny')
$Acl.AddAccessRule($Ar)
Set-Acl $Path $Acl3. Log Audit & IoC Verification Commands
Verify the file version of clfs.sys to ensure the patch has been successfully applied, and audit the system event logs for CLFS-related crashes.
# Check the file version of the CLFS driver
$ClfsPath = '$env:windir\System32\drivers\clfs.sys'
if (Test-Path $ClfsPath) {
$VersionInfo = (Get-Item $ClfsPath).VersionInfo
Write-Host 'CLFS.sys File Version:' $VersionInfo.FileVersion
Write-Host 'Product Version:' $VersionInfo.ProductVersion
} else {
Write-Error 'clfs.sys driver file not found.'
}
# Query Event Viewer for BugCheck events (BSOD) related to clfs.sys
Get-WinEvent -FilterHashtable @{LogName='System'; Id=1001} -ErrorAction SilentlyContinue |
Where-Object {$_.Message -like '*clfs.sys*'} |
Select-Object TimeCreated, Id, Message | Format-Table -AutoSizeBlock Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2025-29824) is a critical Use-After-Free (UAF) flaw residing within the Windows Common Log File System (CLFS) driver (clfs.sys). The root cause lies in the driver's improper reference count management of memory objects when parsing and handling log blocks, metadata blocks, or containers. When the driver fails to track the lifecycle of these objects correctly, a pointer to an already freed memory block remains active. Subsequent operations attempting to access this dangling pointer trigger a Use-After-Free condition, allowing memory corruption in the kernel space.
2. Exploitation Mechanics & Attack Scenario
To exploit this vulnerability, an attacker must first gain local execution privileges on the target system. The attacker then crafts a malicious Base Log File (.blf) and associated container files designed to trigger specific parsing paths within clfs.sys. By invoking CLFS-related APIs (such as CreateLogFile), the attacker forces the driver to allocate and subsequently free a target metadata structure. Using pool spraying techniques, the attacker reclaims the freed memory space with controlled payload data. When the driver dereferences the dangling pointer, it executes attacker-controlled virtual function tables (vtables), leading to arbitrary code execution in kernel mode (Ring 0) and token stealing to escalate privileges to SYSTEM.
3. Infrastructure & Business Impact
With a CVSS score of 7.8 and its inclusion in CISA's Known Exploited Vulnerabilities (KEV) catalog, this vulnerability represents an active threat currently exploited in the wild. Local Privilege Escalation (EoP) vulnerabilities are highly sought after by APT groups and ransomware operators to bypass Endpoint Detection and Response (EDR) agents, dump credentials (e.g., LSASS), and establish persistent administrative control over the compromised host. Successful exploitation can lead to full domain compromise and widespread ransomware deployment across the enterprise network.
Official Vendor Advisories & References
Use after free in Windows Common Log File System Driver allows an authorized attacker to elevate privileges locally.
Frequently Asked SecOps Questions (CVE-2025-29824)
FAQQ1. How critical is CVE-2025-29824 and is it actively exploited in the wild?
CVE-2025-29824 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 19.3%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2025-29824?
Primary impacted vendors include microsoft across windows, windows_server. Scope summary: Most supported versions of Windows 10, Windows 11, and Windows Server (2016, 2019, 2022, 2025) prior to the March 2025 security updates.
Q3. What temporary mitigations or workarounds exist for CVE-2025-29824 before patching?
[Mitigation] Immediately apply the latest cumulative security updates released by Microsoft (March 2025 Patch Tuesday or later). Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2025-29824
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