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

> A race condition in Linux kernel fsnotify allows local attackers to bypass file modification monitoring by causing stale event masks.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100157, BELL-CVE-2026-89595, DEBIAN-CVE-2026-89595, GHSA-h76q-h94r-6qmf, UBUNTU-CVE-2026-89595

## What is CVE-2026-89595?

CVE-2026-89595 is a vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

## Which versions are affected by CVE-2026-89595?


## How do I fix CVE-2026-89595?

Apply the vendor's patch.

## Is CVE-2026-89595 being exploited?

There is no known exploitation of CVE-2026-89595 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89595 and fix it if it is affected.

What it is: CVE-2026-89595 is a vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89595 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89595/ (Markdown: https://insights.sbomify.com/CVE-2026-89595/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89595
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89595
- OSV: https://osv.dev/vulnerability/CVE-2026-89595

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89595/
Summaries are generated and may contain mistakes; the official description above is the record.