Windows Common Log File System (CLFS) Driver Elevation of Privilege Vulnerability (CVE-2023-28252) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTWindows 10, 11, and Windows Server 2008, 2012, 2016, 2019, 2022 utilizing the clfs.sys driver
Local attackers can execute arbitrary code with SYSTEM privileges, fully compromising the host and disabling security controls
Apply the Microsoft April 2023 security updates immediately, or restrict .blf file creation permissions as a temporary workaround
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
The primary remediation is to apply the April 2023 cumulative updates. Use the following PowerShell commands to verify patch status and force updates.
# Check if the required KB patch (e.g., KB5025221 / KB5025239) is installed
Get-HotFix | Where-Object { $_.HotFixID -match 'KB5025221' -or $_.HotFixID -match 'KB5025239' }
# Force Windows Update to download and install missing security patches
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck
Get-WindowsUpdate -AcceptAll -Install -AutoReboot2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict the creation of .blf files in user-writable directories to mitigate local exploitation vectors.
# Restrict 'Everyone' from creating files in public directories to prevent malicious .blf placement
$Path = 'C:\Users\Public\Downloads'
$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
Audit the system for clfs.sys crashes or abnormal driver behavior that may indicate exploitation attempts.
# Query Event Viewer for system crashes (BugCheck) 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 -AutoSize
# Verify the file version of clfs.sys to ensure the patch is active
(Get-Item 'C:\Windows\System32\drivers\clfs.sys').VersionInfo | Select-Object FileVersion, ProductVersionBlock 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-2023-28252) is an out-of-bounds write (CWE-787) and heap-based buffer overflow (CWE-122) vulnerability within the Common Log File System (CLFS.sys) driver, a kernel-mode subsystem in Microsoft Windows. The root cause lies in the driver's failure to properly validate the structure and size metadata of Base Log Files (.blf) during parsing. When a malformed .blf file is loaded, the driver performs out-of-bounds memory writes in the kernel pool, leading to memory corruption.
2. Exploitation Mechanics & Attack Scenario
An attacker must first obtain local execution capabilities on the target system with low-privilege access. The attacker then crafts a malicious .blf file with corrupted metadata fields, such as the Base Record Header or Signatures Offset. When the application calls the CreateLogFile API to open this file, clfs.sys allocates a buffer in the kernel pool and copies the corrupted structure. Due to the lack of bounds checking, the driver overwrites adjacent kernel structures. By carefully grooming the kernel pool, the attacker overwrites critical kernel objects (e.g., token pointers) to elevate privileges to 'NT AUTHORITY\SYSTEM'.
3. Infrastructure & Business Impact
This vulnerability is actively exploited in the wild and is listed in the CISA KEV catalog. It has been observed as a zero-day exploit utilized by ransomware groups (such as Nokoyawa) to bypass endpoint detection and response (EDR) agents, dump credentials, and deploy domain-wide ransomware. Successful exploitation grants full administrative control over the endpoint, posing a severe threat to enterprise infrastructure and business continuity.
Official Vendor Advisories & References
Windows Common Log File System Driver Elevation of Privilege Vulnerability
Frequently Asked SecOps Questions (CVE-2023-28252)
FAQQ1. How critical is CVE-2023-28252 and is it actively exploited in the wild?
CVE-2023-28252 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 48.9%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2023-28252?
Primary impacted vendors include microsoft across windows, windows_server. Scope summary: All supported versions of Windows 10, Windows 11, and Windows Server 2008 through 2022 prior to the April 2023 security updates
Q3. What temporary mitigations or workarounds exist for CVE-2023-28252 before patching?
[Mitigation] Apply the Microsoft April 2023 security updates immediately, or restrict .blf file creation permissions as a temporary workaround 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-2023-28252
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