CVE-2026-83835 in Windows
Summary
by MITRE • 10/14/2026
Buffer over-read in Windows Common Log File System Driver allows an authorized attacker to disclose information locally.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified involves a buffer over-read condition within the Windows Common Log File System driver, commonly referred to as CLFS.sys. This component is integral to the Microsoft Windows operating system architecture, serving as a foundational subsystem for logging and transaction management across various kernel-mode components. The specific flaw arises from improper validation of input parameters or boundary checks when processing data structures passed to the driver by user-space applications or other kernel modules. Because this operation occurs at a low level within the operating system's core infrastructure, it represents a significant deviation from secure coding practices regarding memory access controls. An attacker who has already achieved local execution privileges on the target machine can exploit this flaw to read arbitrary portions of kernel-mode memory that lie beyond the intended buffer boundaries.
From a technical perspective, this vulnerability is classified under CWE-126, which denotes Buffer Over-read. This category encompasses instances where software reads data past the end or before the beginning of a buffer without proper bounds checking. In the context of CLFS.sys, the over-read likely occurs during the parsing or handling of log records and transaction logs. When an attacker crafts specific inputs that trigger this condition, they can cause the driver to copy sensitive memory contents into a user-accessible location or leak them through error messages and return values. This mechanism allows for the extraction of kernel pointers, cryptographic keys, session tokens, or other high-value data residing in protected memory spaces. The exploitation does not require privilege escalation beyond what is already possessed by the attacker but significantly enhances their ability to perform further attacks based on the disclosed information.
The operational impact of this vulnerability centers on confidentiality rather than integrity or availability. By successfully exploiting the buffer over-read, an authorized local user can disclose sensitive system information that would otherwise be inaccessible. This disclosure facilitates subsequent stages of attack chains, such as bypassing kernel patch protection (PatchGuard), defeating address space layout randomization (ASLR) by leaking memory addresses, and extracting credentials stored in secure enclaves or protected storage areas. The ability to read arbitrary kernel memory undermines the isolation guarantees provided by modern operating systems, effectively reducing the security boundary between user-mode applications and the privileged kernel environment. While immediate system stability is not necessarily compromised, as over-reads typically do not cause crashes like buffer overflows might, the long-term risk involves persistent compromise of sensitive data and increased attack surface for advanced persistent threats targeting enterprise environments.
In alignment with industry standards, this vulnerability maps to MITRE ATT&CK technique T1057, which covers Process Discovery, specifically through memory scraping or reading techniques when combined with other exploits. It also relates to T1003, the OS Credential Dumping technique, as leaked kernel data often includes hashes and tokens necessary for lateral movement. To mitigate this risk, organizations should ensure that all Windows systems are updated with the latest security patches provided by Microsoft, which typically include fixes for such driver-level flaws in cumulative updates or out-of-band releases if deemed critical. Administrators must enforce strict least-privilege policies to limit local user accounts from executing untrusted code, thereby reducing the attack surface available to potential exploiters. Additionally, deploying endpoint detection and response solutions that monitor for anomalous memory access patterns by non-system processes can provide an additional layer of defense against exploitation attempts targeting kernel drivers like CLFS.sys.