# CVE-2026-89660: NFSD: Prevent client use-after-free during admin state revocation

> A race condition in the Linux kernel's NFS server allows a use-after-free during client state revocation, potentially leading to code execution or denial of service.

- **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-2026-89660, DEBIAN-CVE-2026-89660, GHSA-xcq6-xf9g-6gc6, UBUNTU-CVE-2026-89660

## What is CVE-2026-89660?

CVE-2026-89660 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 admin state revocation

A stateid holds only a bare pointer to its nfs4_client; a stateid
reference does not pin it.  The client survives only because
__destroy_client() drains its stateids before free_client() runs.

nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(),
which dereferences the client to revoke a stateid and read
clp->cl_minorversion.  A teardown racing the dropped lock can free
the client first.

Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and
EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero.
force_expire_client() ignores it: once its wait for cl_rpc_users to
reach zero has passed, a later pin goes unnoticed.

Under client_lock, skip a client whose cl_time is already zero --
force_expire_client() clears it there before waiting -- otherwise pin
cl_rpc_users before dropping the lock.  The walk then either sees the
expiry and skips, or pins in time for that wait to cover the revoke.

## Which versions are affected by CVE-2026-89660?


## How do I fix CVE-2026-89660?

Apply the vendor's patch.

## Is CVE-2026-89660 being exploited?

There is no known exploitation of CVE-2026-89660 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89660 and fix it if it is affected.

What it is: CVE-2026-89660 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-2026-89660 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-2026-89660/ (Markdown: https://insights.sbomify.com/CVE-2026-89660/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89660
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89660
- OSV: https://osv.dev/vulnerability/CVE-2026-89660

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89660/
Summaries are generated and may contain mistakes; the official description above is the record.