# CVE-2026-89831: f2fs: protect critical_task_priority updates with s_umount

> A race condition in the Linux kernel f2fs filesystem allows local attackers to cause a denial of service by racing sysfs writes with thread teardown.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-89831, GHSA-gh89-f7g4-6qgp, UBUNTU-CVE-2026-89831

## What is CVE-2026-89831?

CVE-2026-89831 is a vulnerability in Linux, published on 16 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:

f2fs: protect critical_task_priority updates with s_umount

The sysfs store path already takes s_umount for GC thread control
entries, and ckpt_thread_ioprio is covered as well.

critical_task_priority also updates checkpoint or GC kthread scheduling
state, but it is not covered by that serialization. It can race with
remount or teardown paths that are stopping those threads.

Protect critical_task_priority sysfs writes with s_umount too.

## Which versions are affected by CVE-2026-89831?


## How do I fix CVE-2026-89831?

Apply the vendor's patch.

## Is CVE-2026-89831 being exploited?

There is no known exploitation of CVE-2026-89831 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89831 and fix it if it is affected.

What it is: CVE-2026-89831 is a vulnerability in Linux, published on 16 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-2026-89831 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-2026-89831/ (Markdown: https://insights.sbomify.com/CVE-2026-89831/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89831
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89831
- OSV: https://osv.dev/vulnerability/CVE-2026-89831

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89831/
Summaries are generated and may contain mistakes; the official description above is the record.