# CVE-2026-89688: nfsd: drop the stateid, not the stateowner, on seqid_op replay retry

> A refcount underflow in the Linux kernel NFS server allows attackers to trigger a use-after-free, 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-2026-89688, DEBIAN-CVE-2026-89688, GHSA-mq7m-fxw5-rr6m, UBUNTU-CVE-2026-89688

## What is CVE-2026-89688?

CVE-2026-89688 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: drop the stateid, not the stateowner, on seqid_op replay retry

In nfs4_preprocess_seqid_op() the stateid is obtained from
nfsd4_lookup_stateid(), which holds a reference on the nfs4_stid
(sc_count) but takes no reference on the stateowner. openlockstateid()
merely casts that stid and likewise takes no reference.

When nfsd4_cstate_assign_replay() returns -EAGAIN (the replay owner is
being torn down, RP_UNHASHED) it has not taken a stateowner reference on
that path. The error handling nevertheless called
nfs4_put_stateowner(stp->st_stateowner), dropping an so_count reference
the function never acquired -- risking a stateowner refcount underflow and
use-after-free -- while leaking the sc_count reference held on the stid.
The leaked stid reference can also stall a concurrent
nfsd4_close_open_stateid() waiting for sc_count to drop.

Drop the reference actually held -- the stid -- before retrying. The
stateowner stays alive through the reference held by the stid. This mirrors
the open path in nfsd4_process_open1(), where the put balances a reference
that path explicitly holds on the stateowner.

## Which versions are affected by CVE-2026-89688?


## How do I fix CVE-2026-89688?

Apply the vendor's patch.

## Is CVE-2026-89688 being exploited?

There is no known exploitation of CVE-2026-89688 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89688 and fix it if it is affected.

What it is: CVE-2026-89688 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-2026-89688 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-2026-89688/ (Markdown: https://insights.sbomify.com/CVE-2026-89688/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89688
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89688
- OSV: https://osv.dev/vulnerability/CVE-2026-89688

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89688/
Summaries are generated and may contain mistakes; the official description above is the record.