# CVE-2026-90037: NFSD: Prevent client use-after-free during close_lru reaping

> A race condition in the Linux kernel NFSD allows attackers to trigger a use-after-free, potentially leading to code execution or privilege escalation.

- **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:** 16 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-101642, BELL-CVE-2026-90037, DEBIAN-CVE-2026-90037, GHSA-cj69-89jw-ggxp, UBUNTU-CVE-2026-90037

## What is CVE-2026-90037?

CVE-2026-90037 is a critical use after free vulnerability in Linux, published on 16 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 close_lru reaping

An nfs4_openowner left on nn->close_lru after its final CLOSE keeps
its last closed stateid in oo_last_closed_stid, holding only a raw
pointer to its nfs4_client. The laundromat reaps timed-out entries,
drops nn->client_lock, and calls nfs4_put_stid(), which dereferences
the client through cl_lock. Nothing pins the client across that
window, so a concurrent force_expire_client() can free it and
nfs4_put_stid() reads freed memory. __destroy_client() hits the same
race, walking clp->cl_openowners without cl_lock.

Pin the client with cl_rpc_users before dropping client_lock, and
skip clients already expiring. __destroy_client() then cleans up its
own close_lru entries through release_last_closed_stateid(), so
teardown no longer races the laundromat.

## Which versions are affected by CVE-2026-90037?


## How do I fix CVE-2026-90037?

Apply the vendor's patch.

## Is CVE-2026-90037 being exploited?

There is no known exploitation of CVE-2026-90037 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90037 and fix it if it is affected.

What it is: CVE-2026-90037 is a critical use after free vulnerability in Linux, published on 16 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-2026-90037 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-2026-90037/ (Markdown: https://insights.sbomify.com/CVE-2026-90037/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90037
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90037
- OSV: https://osv.dev/vulnerability/CVE-2026-90037

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90037/
Summaries are generated and may contain mistakes; the official description above is the record.