# CVE-2026-90236: NFSD: Release the export reference when reaping open stateids

> A reference counting bug in the Linux kernel NFSD module prevents unmounting exports, leading to a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-frqj-gv5h-9hcc, UBUNTU-CVE-2026-90236

## What is CVE-2026-90236?

CVE-2026-90236 is a denial of service vulnerability in Linux, published on 17 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: Release the export reference when reaping open stateids

nfs4_put_stid() releases the svc_export tracked in
nfs4_stid.sc_export, but free_ol_stateid_reaplist() frees open and
lock stateids by calling ->sc_free() directly, bypassing that path.
An open stateid takes an sc_export reference in nfs4_open() and a
lock stateid takes its own in init_lock_stateid(); both reach
free_ol_stateid_reaplist() through their normal teardown, the open
stateid via release_open_stateid() and the lock stateid via
nfsd4_release_lockowner(), each through put_ol_stateid_locked().
The reference is therefore never dropped, pinning the export and
blocking unmount for the lifetime of the stateid.

Release sc_export in free_ol_stateid_reaplist() the way
nfs4_put_stid() does. ->sc_free() runs once per stateid, and a
stateid reaches free_ol_stateid_reaplist() or nfs4_put_stid() but
never both, so the reference is dropped exactly once. Revoked
stateids reach this path with sc_export already cleared by
drop_stid_export(), so they are skipped rather than double-freed.

nfs4_put_stid() itself read sc_export before acquiring cl_lock.
drop_stid_export() clears that field and releases the reference
under cl_lock, so a concurrent revocation could drop the export in
the window between the read and the final put, releasing the same
reference twice. Read sc_export while cl_lock is held so the two
paths serialize and the reference is released exactly once.

## Which versions are affected by CVE-2026-90236?


## How do I fix CVE-2026-90236?

Apply the vendor's patch.

## Is CVE-2026-90236 being exploited?

There is no known exploitation of CVE-2026-90236 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90236 and fix it if it is affected.

What it is: CVE-2026-90236 is a denial of service vulnerability in Linux, published on 17 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-2026-90236 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-2026-90236/ (Markdown: https://insights.sbomify.com/CVE-2026-90236/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90236
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90236
- OSV: https://osv.dev/vulnerability/CVE-2026-90236

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90236/
Summaries are generated and may contain mistakes; the official description above is the record.