# CVE-2026-89658: NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup

> A use-after-free in the Linux kernel NFSD allows attackers to cause denial of service or execute code via race conditions during NFSv4.0 state cleanup.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89658, DEBIAN-CVE-2026-89658, GHSA-mr23-3fxm-cw86, UBUNTU-CVE-2026-89658

## What is CVE-2026-89658?

CVE-2026-89658 is a critical use after free vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup

nfs40_clean_admin_revoked() takes a stateid reference under
clp->cl_lock, drops nn->client_lock, and calls
nfsd4_drop_revoked_stid(), which dereferences the stateid's client
through s->sc_client->cl_lock.  The stateid reference does not pin the
client, so a teardown racing the dropped lock can free the client
while nfsd4_drop_revoked_stid() is still using it.

This cleanup runs from the laundromat, so a periodic sweep can race
force_expire_client() driven by a write to the clients/<id>/ctl file.

Skip a client that is already expiring and otherwise pin it with
cl_rpc_users under client_lock before dropping the lock, matching
nfsd4_revoke_states().

## Which versions are affected by CVE-2026-89658?


## How do I fix CVE-2026-89658?

Apply the vendor's patch.

## Is CVE-2026-89658 being exploited?

There is no known exploitation of CVE-2026-89658 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89658 and fix it if it is affected.

What it is: CVE-2026-89658 is a critical use after free vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89658 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-2026-89658/ (Markdown: https://insights.sbomify.com/CVE-2026-89658/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89658
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89658
- OSV: https://osv.dev/vulnerability/CVE-2026-89658

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89658/
Summaries are generated and may contain mistakes; the official description above is the record.