# CVE-2026-89692: nfsd: clear CALLBACK_RUNNING on failed delegation recall queue

> A logic error in the Linux kernel NFS server leaves a flag set on failed recall attempts, causing subsequent delegations to stall and leading to denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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-2026-89692, DEBIAN-CVE-2026-89692, GHSA-mcqc-fm6v-5h2r, UBUNTU-CVE-2026-89692

## What is CVE-2026-89692?

CVE-2026-89692 is a high-severity denial of service 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: clear CALLBACK_RUNNING on failed delegation recall queue

nfsd_break_one_deleg() sets NFSD4_CALLBACK_RUNNING via test_and_set_bit
at entry to serialize recall work, then calls nfsd4_run_cb() to queue
the recall.  When the queue attempt fails the refcount bump is undone,
but the RUNNING bit is left set.  The only site that clears the bit is
nfsd41_destroy_cb() (fs/nfsd/nfs4callback.c), which runs from the
workqueue and is therefore unreachable when nothing was queued.

The bit becomes a permanent latch on dp->dl_recall.cb_flags: every
subsequent break_lease() on the same delegation hits the early-return
guard in nfsd_break_one_deleg() and silently skips the recall, so the
delegation is never broken and the conflicting open or lock stalls.

Fix by clearing NFSD4_CALLBACK_RUNNING on the !queued branch alongside
the refcount_dec.

## Which versions are affected by CVE-2026-89692?


## How do I fix CVE-2026-89692?

Apply the vendor's patch.

## Is CVE-2026-89692 being exploited?

There is no known exploitation of CVE-2026-89692 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89692 and fix it if it is affected.

What it is: CVE-2026-89692 is a high-severity denial of service 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-2026-89692 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-2026-89692/ (Markdown: https://insights.sbomify.com/CVE-2026-89692/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89692
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89692
- OSV: https://osv.dev/vulnerability/CVE-2026-89692

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89692/
Summaries are generated and may contain mistakes; the official description above is the record.