CVE-2024-49138
Microsoft Windows Common Log File System (CLFS) Driver Heap-Based Buffer Overflow Vulnerability
Description
CVE-2024-49138 is a high-severity elevation of privilege vulnerability in the Windows Common Log File System (CLFS) driver affecting virtually all supported versions of Windows and Windows Server. The flaw allows a locally authenticated attacker with low privileges to escalate to SYSTEM-level access by exploiting a heap-based buffer overflow in the CLFS driver. With a CVSS v3.1 base score of 7.8, the vulnerability requires local access and low privileges but no user interaction. CISA has added CVE-2024-49138 to the Known Exploited Vulnerabilities catalog with a remediation deadline of December 31, 2024, and its EPSS score of 85.68% at the 99.4th percentile indicates an extremely high probability of exploitation across the Windows ecosystem.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | windows 10 1507 | < 10.0.10240.20857 |
| microsoft | windows 10 1607 | < 10.0.14393.7606 |
| microsoft | windows 10 1809 | < 10.0.17763.6659 |
| microsoft | windows 10 21h2 | < 10.0.19044.5247 |
| microsoft | windows 10 22h2 | < 10.0.19045.5247 |
| microsoft | windows 11 22h2 | < 10.0.22621.4602 |
| microsoft | windows 11 23h2 | < 10.0.22631.4602 |
| microsoft | windows 11 24h2 | < 10.0.26100.2605 |
| microsoft | windows server 2008 | -; r2; sp2 |
| microsoft | windows server 2012 | -; r2 |
| microsoft | windows server 2016 | < 10.0.14393.7606 |
| microsoft | windows server 2019 | < 10.0.17763.6659 |
| microsoft | windows server 2022 | < 10.0.20348.2966 |
| microsoft | windows server 2022 23h2 | < 10.0.25398.1308 |
| microsoft | windows server 2025 | < 10.0.26100.2605 |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-49138(Patch, Vendor Advisory)
- https://packetstorm.news/files/id/190585/(Exploit, VDB Entry)
- https://www.exploit-db.com/exploits/52270(Exploit, VDB Entry)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-49138(US Government Resource)
Weakness Type
CWE-269: Improper Privilege Management
CVE-2024-49138 is associated with CWE-269 (Improper Privilege Management), which describes vulnerabilities where a product does not properly assign, modify, track, or check privileges for actors, creating an unintended sphere of control. In the Windows CLFS driver, improper handling of log file structures allows a low-privileged user to corrupt kernel memory in a controlled manner, ultimately granting the attacker SYSTEM-level privileges. The CLFS driver operates in kernel mode, and its failure to properly validate and manage memory operations means that any local user can leverage the vulnerability to bypass all privilege boundaries enforced by the operating system.
Impact Analysis
The impact of CVE-2024-49138 is severe across all CIA dimensions. Confidentiality is fully compromised because SYSTEM-level access grants the attacker unrestricted ability to read any data on the machine, including credentials stored in the Security Account Manager (SAM) database, DPAPI-protected secrets, cached domain credentials, and all user files. In enterprise environments, compromising a single machine at SYSTEM level often enables lateral movement through credential harvesting.
Integrity faces maximum impact as SYSTEM privileges allow the attacker to modify any file, registry key, or system configuration on the host. This includes disabling security software, installing rootkits, modifying audit logs to cover tracks, creating persistence mechanisms, and tampering with Group Policy objects on domain controllers.
Availability is fully at risk since SYSTEM access enables the attacker to disable critical services, deploy ransomware, corrupt the operating system, or render the machine inoperable. The attack vector is local (AV:L), meaning the attacker needs existing access to the system, but only low-level privileges are required (PR:L). Public exploit code is available on PacketStorm and Exploit-DB, significantly lowering the barrier to exploitation. The breadth of affected Windows versions — from Windows 10 through Windows Server 2025 — means the vulnerability impacts nearly every Windows deployment worldwide.
Exploit Maturity
CVE-2024-49138 demonstrates very high exploit maturity with confirmed active exploitation. CISA has added it to the Known Exploited Vulnerabilities catalog, confirming in-the-wild exploitation. The EPSS score of 85.68% at the 99.4th percentile places this vulnerability among the most likely to be exploited across the entire vulnerability landscape.
Public exploit code is readily available. A working proof-of-concept has been published on PacketStorm and Exploit-DB, making exploitation accessible to a wide range of threat actors beyond sophisticated groups. The Windows CLFS driver has been a recurring target for privilege escalation exploits, with multiple CLFS vulnerabilities exploited in the wild in recent years. Ransomware operators frequently use CLFS elevation of privilege vulnerabilities to escalate from initial user-level access to SYSTEM, enabling them to disable security tools and deploy encryption payloads. While CISA has not yet confirmed a direct ransomware association for this specific CVE, the exploitation pattern and availability of public exploits make it highly likely that ransomware groups are leveraging CVE-2024-49138 in their attack chains.
Remediation
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Apply the December 2024 Microsoft security update immediately across all affected Windows systems. The patch is available through Windows Update, WSUS, and the Microsoft Update Catalog. Consult the Microsoft Security Response Center advisory for version-specific KB article numbers and deployment guidance.
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Prioritize patching based on exposure by addressing internet-facing servers and systems accessible to untrusted users first. Domain controllers, file servers, and jump servers should receive the highest priority due to the impact of SYSTEM-level compromise on these critical assets.
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Monitor for exploitation attempts by enabling Windows event logging for CLFS-related operations. Review Security and System event logs for unusual process creation events running as SYSTEM from unexpected parent processes. Deploy endpoint detection and response solutions that can detect known exploitation techniques targeting the CLFS driver.
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Implement least-privilege access controls as a defense-in-depth measure. Minimize the number of user accounts with local logon rights on servers. Use Group Policy to restrict local logon and remote desktop access to authorized administrators only. This reduces the pool of accounts that could potentially exploit the vulnerability.
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Conduct credential hygiene assessments on systems that may have been compromised before patching. Reset local administrator passwords, rotate service account credentials, and invalidate any Kerberos tickets that may have been generated during a compromise window.
Technical Details
CVE-2024-49138 is a heap-based buffer overflow vulnerability in the Windows Common Log File System (CLFS) driver, a kernel-mode component responsible for managing transactional log files. The CVSS v3.1 vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, indicating a local attack that requires low privileges and no user interaction, with high impact across all CIA dimensions.
The CLFS driver (clfs.sys) processes Base Log File (BLF) structures that contain metadata blocks, container contexts, and client contexts. The vulnerability exists in the driver's handling of specific fields within these log file structures. By crafting a malicious BLF file or manipulating CLFS API calls, an attacker can trigger a heap-based buffer overflow in kernel pool memory. This corruption allows the attacker to overwrite adjacent kernel objects, achieving arbitrary read/write primitives in kernel memory.
With kernel memory read/write capabilities, the attacker modifies the token of their process to duplicate the privileges of the SYSTEM process, effectively granting their user-mode process unrestricted access to the entire system. The exploitation technique leverages well-known Windows kernel exploitation patterns involving pool corruption and token manipulation.
The scope is unchanged (S:U) because the vulnerability operates within the Windows kernel security context, but achieving SYSTEM privileges effectively means complete control over the local machine. Affected versions span the entire supported Windows product line, from Windows 10 version 1507 through Windows Server 2025, highlighting how deeply embedded the CLFS driver is in the Windows architecture.
Frequently Asked Questions
What is CVE-2024-49138?
CVE-2024-49138 is a high-severity elevation of privilege vulnerability in the Windows Common Log File System (CLFS) driver. It allows a low-privileged local attacker to escalate to SYSTEM-level privileges through a heap-based buffer overflow in the kernel-mode CLFS driver.
Which Windows versions are affected by CVE-2024-49138?
Virtually all supported Windows versions are affected, including Windows 10 (all supported versions), Windows 11 (22H2, 23H2, 24H2), and Windows Server 2008 through Windows Server 2025. Organizations should apply the December 2024 security update to all Windows systems.
Are public exploits available for CVE-2024-49138?
Yes. Public exploit code has been published on PacketStorm and Exploit-DB, making the vulnerability accessible to a broad range of attackers. This significantly increases the urgency of applying the security update.
Can CVE-2024-49138 be exploited remotely?
No. CVE-2024-49138 requires local access to the target system. However, in practice, attackers typically chain this vulnerability with a remote access vulnerability or phishing-based initial access to first gain a foothold on the system, then escalate privileges using this CLFS flaw.
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