# CVE-2026-89686: nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke

> A race condition in the Linux kernel NFS server allows remote attackers to cause a denial of service via a BUG_ON crash during concurrent delegation revokes.

- **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:** 21 Oct 2026
- **Also known as:** AZL-100455, BELL-CVE-2026-89686, DEBIAN-CVE-2026-89686, GHSA-8hmx-j653-mwq6, UBUNTU-CVE-2026-89686

## What is CVE-2026-89686?

CVE-2026-89686 is a critical 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: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke

nfsd4_alloc_layout_stateid reads fp->fi_deleg_file without holding
fi_lock when the parent stateid is a delegation. A concurrent delegation
revoke via the laundromat can clear fi_deleg_file under fi_lock, causing
nfsd_file_get() to return NULL and triggering the BUG_ON.

This race is client-reachable: two NFS clients can trigger it by having
one hold a delegation while another opens the same file to force a
recall. When the first client doesn't respond to the recall, the
laundromat revokes it. A concurrent LAYOUTGET from any client using the
delegation stateid hits the race window.

Fix this by taking fi_lock around the fi_deleg_file read in the
SC_TYPE_DELEG path, matching the locking discipline of the
find_any_file() arm, and replacing the BUG_ON with a graceful error
return that cleans up the partially-initialized layout stateid.

## Which versions are affected by CVE-2026-89686?


## How do I fix CVE-2026-89686?

Apply the vendor's patch.

## Is CVE-2026-89686 being exploited?

There is no known exploitation of CVE-2026-89686 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89686 and fix it if it is affected.

What it is: CVE-2026-89686 is a critical 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-2026-89686 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-2026-89686/ (Markdown: https://insights.sbomify.com/CVE-2026-89686/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89686
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89686
- OSV: https://osv.dev/vulnerability/CVE-2026-89686

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89686/
Summaries are generated and may contain mistakes; the official description above is the record.