A race condition in the Linux kernel’s fsnotify subsystem can leave the cached object mask stale after concurrent fanotify or inotify mark updates. When a mark gains an event bit, the kernel may skip recalculation if the cached aggregate already contains that bit, but a concurrent update on the same connector can cause the cached mask to be published without the new bit. The result is that a watcher may miss FAN_MODIFY or IN_MODIFY events even though the file has been modified. The flaw does not provide direct control over memory, data, or code execution, so it does not lead to privilege escalation, but it can cause application logic errors or data loss when real‑time change notifications are relied upon.

The issue affects all Linux kernel releases that contain the vulnerable fsnotify logic, beginning with kernel v6.12.95 and earlier until the patch is back‑ported. Distributions shipping those kernels, or any kernel that has not incorporated the fix, are impacted.

The CVSS base score is 2.5, the EPSS score is < 1%, and the vulnerability is not listed in the CISA KEV catalog. The EPSS score of < 1% indicates a very low probability of exploitation. Exploitation requires a race between two locally executed threads that add or modify fanotify or inotify marks; thus it is limited to local or privileged processes. Because the consequence is limited to missing modification notifications rather than escalation or arbitrary code execution, the overall risk is low. However, applications that depend on precise file‑change events may behave incorrectly or lose data when the bug manifests.