Windows Common Log File System Driver Elevation of Privilege Vulnerability
CVE-2026-40397 is an elevation-of-privilege vulnerability in the Windows Common Log File System (CLFS) driver caused by an integer underflow (wrap or wraparound). Microsoft states that the flaw allows an authorized attacker to elevate privileges locally. The issue affects the Windows Common Log File System Driver and stems from improper handling of integer arithmetic that can underflow during driver processing, creating a path to privilege escalation on the local system.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
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.
Recent activity
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.
The version that knows your environment.
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.