CVE-2025-29824: Microsoft Windows Common Log File System (CLFS) Driver Use-After-Free Vulnerability

CVE-2025-29824 is a use-after-free vulnerability in the Microsoft Windows Common Log File System (CLFS) Driver. An authorized attacker who already has some level of access on a system can exploit it to elevate privileges locally. Because this flaw has been observed in ransomware campaigns, it poses a clear risk of full system compromise once initial access is obtained. Confirm all version and patch details against the Microsoft advisory before acting.

Defenders should treat this as a high-priority local elevation-of-privilege issue on Windows hosts. The CISA summary and required action emphasize applying vendor mitigations promptly or discontinuing use if none are available, and following BOD 22-01 guidance where cloud services are involved.

How it works

The vulnerability is classified as CWE-416 (use-after-free). In a use-after-free condition, memory that has been freed is later referenced again by the driver. An attacker who can trigger the free and then control the subsequent use of that memory can corrupt kernel structures or redirect execution flow.

According to the CISA summary, the attacker must already be authorized on the system (local access). From that foothold the attacker abuses the CLFS driver to gain higher privileges, typically SYSTEM-level rights. Exact trigger conditions, memory layouts, or exploit sequences are not provided in the public facts and must be confirmed against the vendor advisory; treat any public proof-of-concept claims with caution until verified.

Am I affected? How to find it in your systems

The CLFS driver is a core component of Microsoft Windows and is present on most modern Windows client and server installations that use the Common Log File System for logging and recovery operations. It typically runs in kernel mode on endpoints, servers, and virtual machines.

• Inventory all Windows systems (workstations, servers, domain controllers, cloud-hosted Windows instances) via asset management, SCCM/Intune, or vulnerability scanners that report installed OS builds and hotfixes.
• Confirm the presence of the CLFS driver (clfs.sys) and its loaded state; check driver version and file hashes against the ranges listed in the Microsoft security update guide.
• Review configurations that rely heavily on transactional logging or CLFS-based features, though the facts do not limit the vulnerability to specific optional components.
• Look for telemetry indicators of exploitation: unexpected privilege escalations, anomalous process creations from low-privilege contexts, kernel crashes or blue screens involving clfs.sys, and ransomware-related behaviors such as rapid file encryption after a local privilege jump. Correlate with EDR alerts for local elevation-of-privilege techniques.

Because exact affected builds are not listed here, cross-check every host against the official Microsoft advisory rather than relying on generic Windows version numbers.

How to remediate

Patch first. Apply the security update Microsoft has released for this CVE as soon as it is available in your patch-management pipeline. Follow the vendor’s installation and reboot guidance exactly.

• Deploy the update through WSUS, Microsoft Update, Intune, or your enterprise patching tool; prioritize internet-facing and high-value systems.
• After installation, verify the updated driver version and that the system is no longer flagged by vulnerability scanners.
• For cloud-hosted Windows instances, also follow applicable BOD 22-01 guidance as directed by CISA.
• If mitigations beyond the patch are published by Microsoft, implement them; otherwise the primary remediation is the vendor update itself.

Once patched, continue normal hardening: least-privilege accounts, application control, and kernel-mode code integrity where feasible.

If you can't patch immediately

Until the vendor update can be applied, reduce the attack surface and increase detection.

• Segment systems so that a compromised low-privilege account cannot easily reach high-value assets; restrict lateral movement with network controls and host firewalls.
• Apply virtual patching or WAF/IPS rules if your security tools offer signatures for CLFS-related elevation attempts (confirm rule coverage with the vendor).
• Disable or limit non-essential use of CLFS features only if Microsoft documents a safe configuration change; do not invent work-arounds.
• Heighten monitoring: enable detailed process-creation and privilege-escalation logging, forward kernel and security events to a SIEM, and alert on any local elevation that precedes ransomware indicators.
• If no mitigations are available and the risk is unacceptable, CISA guidance allows discontinuing use of the product until a fix can be installed.

If your data may have been exposed

Actively exploited elevation-of-privilege vulnerabilities are frequently used by ransomware operators to gain full control and encrypt or exfiltrate data. If you have evidence of exploitation or ransomware activity on affected hosts, assume potential data exposure, isolate the systems, preserve forensic images, and begin incident-response procedures. As a quick check for previously leaked credentials, you can run a free exposure scan of your email addresses against known breach data sets to identify accounts that may need password resets or additional monitoring.