CVE-2026-89595

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

fsnotify: Fix stale object mask after concurrent mark updates

When a mark gets a new event bit, fanotify and inotify may avoid

recalculating the object mask if the cached aggregate already contains that

bit. This is racy with a recalculation triggered by a concurrent update to

another mark on the same connector.

The concurrent scan can read the mark before the new bit is added, while

the updater reads the old aggregate before that scan publishes its result.

The updater then skips recalculation and the scan publishes a mask without

the bit, leaving the object mask stale after both updates complete.

This can be reproduced with two fanotify groups watching the same inode:

one thread removes FAN_MODIFY from one existing mark while another thread

adds FAN_MODIFY to the other mark. After both fanotify_mark() calls return,

writes can fail to produce FAN_MODIFY for the group whose mark now contains

the bit. This was reprod

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References