CVE-2026-40407 in Windows
Summary
by MITRE • 05/12/2026
Heap-based buffer overflow in Windows Common Log File System Driver allows an authorized attacker to elevate privileges locally.
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Analysis
by VulDB Data Team • 05/19/2026
A heap-based buffer overflow vulnerability exists within the Windows Common Log File System Driver component that enables authenticated attackers to achieve local privilege escalation. This flaw resides in the kernel-mode driver responsible for handling common log file system operations, specifically when processing malformed input data through the log file parsing routines. The vulnerability stems from insufficient bounds checking during heap memory allocation and data copying operations, allowing an attacker to overwrite adjacent memory locations in the driver's heap space. The affected driver component typically processes log file data structures that contain user-supplied information, creating an attack surface where malicious input can trigger the overflow condition when the driver attempts to store or manipulate log entries.
The technical exploitation of this vulnerability requires an attacker to first establish a valid user session on the target system, as the privilege escalation occurs within the kernel context where the driver operates. During normal operation, the Common Log File System Driver receives log data from various system components and applications, processing this information through heap-based memory allocations. When the driver encounters malformed or oversized log entries, the insufficient input validation causes the heap memory allocation routines to write beyond the allocated buffer boundaries, potentially overwriting critical heap metadata or adjacent memory structures. This heap corruption can lead to arbitrary code execution within the kernel context, providing the attacker with SYSTEM-level privileges that are normally restricted to privileged system processes.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it represents a significant security weakness in the Windows kernel subsystem that handles logging operations. Attackers can leverage this flaw to bypass standard security controls and gain unauthorized access to sensitive system resources, potentially enabling further attacks such as credential theft, system persistence mechanisms, or lateral movement within the network. The vulnerability affects multiple Windows versions including windows server 2016, windows server 2019, and windows 10, making it particularly concerning for enterprise environments where these systems are commonly deployed. The attack vector requires local access with user credentials, but the privilege escalation to SYSTEM level provides attackers with complete control over the affected system.
Mitigation strategies should focus on immediate patch application from microsoft, which addresses the heap overflow through proper input validation and bounds checking mechanisms. Organizations should implement the principle of least privilege by restricting user access to logging components and monitoring for unusual log file processing activities. Additionally, the vulnerability aligns with attack techniques described in the attack pattern taxonomy under the privilege escalation category, specifically targeting kernel-mode exploitation methods that leverage memory corruption flaws. Security teams should monitor for potential exploitation attempts through unusual kernel memory access patterns and implement defensive measures such as driver signature enforcement and heap protection mechanisms. The vulnerability demonstrates characteristics consistent with cwe-121 heap-based buffer overflow, where insufficient bounds checking allows data to be written beyond the boundaries of allocated heap memory regions, creating opportunities for memory corruption and privilege escalation attacks.