Skip to main content

Severity by source

NVD PRIMARY
7.8 HIGH
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
vuln.today AI
7.8 HIGH

Local authenticated low-priv access with no user interaction (AV:L/PR:L/UI:N); heap overflow in a kernel driver yields SYSTEM control, so full C/I/A impact.

3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.0 AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

2
Analysis Generated
Jul 23, 2026 - 22:00 vuln.today
CVE Published
May 12, 2026 - 16:58 nvd
HIGH 7.8

DescriptionCVE.org

Heap-based buffer overflow in Windows Common Log File System Driver allows an authorized attacker to elevate privileges locally.

AnalysisAI

Local privilege escalation in the Windows Common Log File System (CLFS) driver lets an already-authenticated low-privileged user corrupt heap memory to gain SYSTEM-level control across a broad range of Windows client and server releases (Windows 10 1607 through Windows 11 26H1, Server 2012 through Server 2025). Exploitation is CVSS 7.8 with total technical impact per CISA SSVC, but SSVC records no observed exploitation and EPSS is very low (0.04%), and no public exploit was identified at time of analysis. A vendor patch is available from Microsoft (MSRC).

Technical ContextAI

The Common Log File System (clfs.sys) is a kernel-mode general-purpose logging subsystem shipped with all supported Windows versions, used by applications and the OS to create and manage transactional log files. The flaw is CWE-122 (heap-based buffer overflow): malformed input processed by the driver writes past an allocated kernel heap buffer, corrupting adjacent kernel memory. Because CLFS runs in kernel context (Ring 0), controlled heap corruption can be leveraged to overwrite kernel structures and hijack execution as SYSTEM. The CPE set confirms the affected component spans the Microsoft Windows platform itself (Windows 10 1607/1809/21H2/22H2, Windows 11 22H3/23H2/24H2/25H2/26H1, and Windows Server 2012 through 2025), consistent with CLFS being a core OS driver rather than an optional feature.

RemediationAI

Apply the Microsoft security update for CVE-2026-40407 via Windows Update or WSUS; this is the primary and complete fix - Vendor-released patch confirmed per Microsoft MSRC (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40407). Install at minimum the fixed build for your edition (e.g. 10.0.26100.8457 for Windows 11 24H2, 10.0.22631.7079 for 23H2, 10.0.19045.7291 for Windows 10 22H2, 6.2.9200.26079 for Server 2012, 10.0.20348.5139 for Server 2022). CLFS cannot be safely disabled as a general workaround because the OS and many applications depend on it, so there is no clean feature-toggle mitigation; until patched, reduce risk by limiting who can obtain local/interactive or low-privileged code execution on the host - enforce least privilege, restrict local logon and RDP on shared/multi-user systems, and monitor EDR for anomalous CLFS/.blf activity and kernel-integrity alerts, accepting that these controls only shrink the attacker pool rather than close the flaw. Additional references: https://vuldb.com/vuln/363198 and https://nvd.nist.gov/vuln/detail/CVE-2026-40407.

CVE-2026-33824 CRITICAL POC
9.8 Apr 14

Remote code execution in Windows IKE Extension (Internet Key Exchange) via double free memory corruption allows unauthen

CVE-2026-56155 HIGH POC
7.8 Jul 14

Local privilege escalation in Microsoft Active Directory Federation Services (AD FS) lets an already-authenticated low-p

CVE-2026-32202 MEDIUM POC
4.3 Apr 14

Windows Shell protection mechanism failure (CVE-2026-32202) allows remote attackers to perform spoofing attacks over a n

CVE-2026-49798 CRITICAL POC
9.3 Jul 14

Local privilege escalation in the Microsoft Windows Kernel allows an unauthorized attacker to gain elevated (SYSTEM-leve

CVE-2026-54128 HIGH POC
8.4 Jul 14

Local code execution in the Windows DHCP Client service stems from a use-after-free (CWE-416) memory-corruption flaw aff

CVE-2026-50518 CRITICAL
9.8 Jul 14

Remote code execution in the Microsoft Windows DHCP Server role allows an unauthenticated network attacker to run arbitr

CVE-2026-50655 HIGH POC
7.8 Jul 14

Local code execution in the Windows Media component of supported Windows 10, Windows 11, and Windows Server (2016 throug

CVE-2026-54992 HIGH POC
7.8 Jul 14

Local privilege escalation via heap-based buffer overflow in the Windows Message Queuing (MSMQ) Queue Manager component

CVE-2026-50489 HIGH POC
7.8 Jul 14

Local privilege escalation in Microsoft Windows Win32K lets an authenticated low-privileged user corrupt kernel heap mem

CVE-2026-50667 HIGH POC
7.0 Jul 14

Local privilege escalation in the Windows NTFS file system driver lets an authenticated low-privileged user win a race c

CVE-2026-57092 CRITICAL
9.9 Jul 14

Elevation of privilege in the Windows Hyper-V virtual network switch (VMSwitch) lets an authenticated attacker operating

CVE-2026-56190 CRITICAL
9.8 Jul 14

Remote code execution in Microsoft Windows Remote Desktop (RDP) allows an unauthorized network attacker to run arbitrary

Share

CVE-2026-40407 vulnerability details – vuln.today

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy