CVE-2024-6768: Windows CLFS.sys DoS Vulnerability

CVE-2024-6768 Overview

CVE-2024-6768 is a denial-of-service vulnerability in the Common Log File System driver (CLFS.sys) shipped with multiple Microsoft Windows releases. An authenticated low-privilege local user can craft input that forces a call to the KeBugCheckEx function, triggering a Blue Screen of Death (BSoD) and crashing the host. The flaw is classified under CWE-1284: Improper Validation of Specified Quantity in Input. Fortra published advisory FR-2024-001 describing the issue, and detection and mitigation scripts have been released by third-party researchers.

Critical Impact

Any authenticated local user can repeatedly crash an affected Windows host, disrupting availability of workstations, domain controllers, and member servers running vulnerable versions of CLFS.sys.

Affected Products

• Microsoft Windows 10 and Windows 11
• Microsoft Windows Server 2016, 2019, and 2022
• Systems loading the vulnerable CLFS.sys driver

Discovery Timeline

• 2024-08-12 - CVE-2024-6768 published to the National Vulnerability Database
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2024-6768

Vulnerability Analysis

The Common Log File System (CLFS) is a general-purpose logging subsystem implemented in the kernel-mode driver CLFS.sys. The driver exposes logging primitives used by both kernel components and user-mode applications through documented APIs. The vulnerability stems from improper validation of a quantity field supplied in attacker-controlled log data ([CWE-1284]). When the driver processes the malformed value, internal consistency checks fail and the kernel invokes KeBugCheckEx, halting the system with a bug check.

Because KeBugCheckEx is the standard kernel routine used to terminate execution on unrecoverable errors, the result is an immediate Blue Screen of Death and forced reboot. Exploitation does not require administrative rights, and the operation can be repeated as soon as the host returns to service, producing a sustained denial of service condition against availability.

Root Cause

The root cause is missing validation of a size or count value parsed from a CLFS structure. The driver trusts the supplied quantity and reaches a code path that detects an inconsistent kernel state, deliberately triggering KeBugCheckEx instead of safely returning an error to user mode.

Attack Vector

The attack vector is local. A standard user account interacts with the CLFS API or opens a crafted log file, passing the malformed data into CLFS.sys. No user interaction from another principal is required. The vulnerability does not provide code execution or information disclosure - the impact is restricted to host availability. Technical details and a proof-of-concept walkthrough are documented in the Fortra Security Advisory FR-2024-001.

Detection Methods for CVE-2024-6768

Indicators of Compromise

• Unexpected KeBugCheckEx bug checks referencing CLFS.sys in the faulting module field of the resulting minidump.
• Microsoft-Windows-Kernel-Power Event ID 41 entries indicating unexpected shutdowns shortly after a low-privilege process accessed CLFS APIs.
• Creation of unusual .blf or container log files in user-writable directories immediately before a crash.

Detection Strategies

• Inspect MEMORY.DMP and minidumps under %SystemRoot%\Minidump for bug checks where the faulting driver is CLFS.sys.
• Correlate process execution telemetry with subsequent host reboots to identify low-privilege processes that consistently precede crashes.
• Apply the Vicarius Detection Script for CVE-2024-6768 to enumerate affected Windows builds across the estate.

Monitoring Recommendations

• Forward Windows System and Application event logs to a central platform and alert on repeated Event ID 1001 (BugCheck) entries citing CLFS.
• Track the file version of C:\Windows\System32\drivers\CLFS.sys across endpoints and flag hosts still running pre-patch builds.
• Baseline normal CLFS usage by service accounts so anomalous interactions from interactive user sessions are surfaced quickly.

How to Mitigate CVE-2024-6768

Immediate Actions Required

• Inventory all Windows 10, Windows 11, and Windows Server 2016/2019/2022 hosts and confirm CLFS.sys version against the patched build.
• Restrict interactive logon on high-value servers to reduce the population of accounts that can trigger the bug.
• Deploy the Vicarius Mitigation Script for CVE-2024-6768 where applicable to compensate until patching completes.

Patch Information

Microsoft addresses CLFS driver issues through monthly cumulative updates delivered via Windows Update and the Microsoft Update Catalog. Apply the latest cumulative update for each affected Windows release and reboot to load the updated CLFS.sys. Refer to the Fortra Security Advisory FR-2024-001 for the technical write-up associated with this CVE.

Workarounds

• Limit local logon rights and remove unnecessary standard user accounts from shared and high-availability servers.
• Enable kernel crash dump collection so that any exploitation attempt produces forensic artifacts for investigation.
• Use application allowlisting to block untrusted binaries that could invoke the CLFS API with crafted log data.

# Configuration example: query the installed CLFS.sys version on a Windows host
powershell -Command "(Get-Item C:\Windows\System32\drivers\CLFS.sys).VersionInfo | Format-List FileVersion,ProductVersion"