EUVD-2026-56641
GHSA-9vgg-r37x-xw5c
Severity by source
AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Local attack vector and low privilege confirmed by description; AC:H reflects TOCTOU race requirement; full CIA impact from SYSTEM-level escalation with no scope change.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Time-of-check time-of-use (toctou) race condition in Windows Common Log File System Driver allows an authorized attacker to elevate privileges locally.
AnalysisAI
Privilege escalation via a time-of-check time-of-use (TOCTOU) race condition in the Windows Common Log File System (CLFS) Driver affects a broad range of Windows client and server versions from Server 2012 through Windows 11 25H2/26H1. A low-privileged local attacker can exploit the race window to gain SYSTEM-level access, achieving full confidentiality, integrity, and availability impact on the host. No public exploit code or CISA KEV listing is identified at time of analysis; vendor patch is available from Microsoft via the MSRC update guide.
Technical ContextAI
The Windows Common Log File System (CLFS) is a kernel-mode driver (clfs.sys) that provides a general-purpose, high-performance logging subsystem used by Windows internals, transaction managers, and applications. TOCTOU vulnerabilities in CLFS arise when the kernel checks a resource state at one point in time but acts on it at a later point, creating a race window exploitable by a concurrent thread or process running at low privilege. The formally listed weakness is CWE-125 (Out-of-bounds Read), yet the vulnerability description specifically names CWE-367-class TOCTOU behavior, and the associated tags reference both 'Information Disclosure' and 'Buffer Overflow' - suggesting the race condition may produce an out-of-bounds memory access as its immediate consequence, which is then leveraged for privilege escalation. CLFS LPE vulnerabilities follow a well-documented exploit pattern in Windows: winning the race window corrupts a kernel structure or log block, enabling an attacker to overwrite security-sensitive memory. Affected CPE covers Windows NT 10.0/6.3/6.2 kernel families across client and server SKUs.
RemediationAI
Apply the Microsoft security update addressing CVE-2026-62728, available through Windows Update, WSUS, and the Microsoft Update Catalog; the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62728 provides direct download links for each affected build. Exact patched build numbers are confirmed per the EUVD affected-versions data above (e.g., Windows 10 22H2 patched at 10.0.19045.7663, Windows Server 2025 at 10.0.26100.33296). For systems that cannot be patched immediately, restrict interactive and remote logon rights to the minimum set of accounts, since the attack requires a low-privileged local session; removing unnecessary local user accounts or service accounts reduces the pool of potential exploiters. Endpoint detection tooling should be configured to monitor for anomalous CLFS driver interactions (e.g., unusual NtCreateLogFile or ClfsCreateLogFile call patterns from non-system processes). Note that neither workaround eliminates the vulnerability; they only reduce exploitation opportunity until patching is feasible.
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Same weakness CWE-125 – Out-of-bounds Read
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today