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CVE-2026-40397 is a local elevation-of-privilege vulnerability in the Windows Common Log File System (CLFS) driver. The flaw is attributed to an integer underflow condition in the driver and is also described as leading to a heap-based buffer overflow during CLFS processing. A locally authenticated attacker with low privileges can exploit the vulnerability without user interaction to corrupt memory in kernel context and elevate execution to SYSTEM. Microsoft assessed the issue as Important and "Exploitation More Likely."
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
3 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An elevation of privilege vulnerability in the Windows Common Log File System driver, notable because CLFS has historically been used as a SYSTEM-level escalation primitive.
An important Windows Common Log File System Driver elevation of privilege vulnerability that Microsoft determined is more likely to be exploited.
A Windows Common Log File System Driver local elevation of privilege vulnerability caused by integer underflow, allowing an authorized attacker with low privileges to gain SYSTEM privileges.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.