# CVE-2026-89679: nfsd: fix null dereference in nfsd4_setattr for deleg timestamp attrs

> A remote attacker can cause a kernel crash in the Linux NFS server by sending a specially crafted SETATTR request with a special stateid.

- **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-2026-89679, DEBIAN-CVE-2026-89679, GHSA-8j83-qm9m-m369, UBUNTU-CVE-2026-89679

## What is CVE-2026-89679?

CVE-2026-89679 is a high-severity 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 null dereference in nfsd4_setattr for deleg timestamp attrs

When a SETATTR request includes FATTR4_WORD2_TIME_DELEG_ACCESS or
FATTR4_WORD2_TIME_DELEG_MODIFY in the attribute bitmap, nfsd4_setattr()
sets deleg_attrs=true and calls nfs4_preprocess_stateid_op() to validate
the stateid.

If the client supplies the NFSv4 "one stateid" (all-0xFF bytes),
check_special_stateids() returns nfs_ok without populating the output
nfs4_stid pointer, because the special-stateid path in
nfs4_preprocess_stateid_op() jumps to done: with s==NULL, and the
"if (s)" block that would set *cstid is skipped. The local variable `st`
remains NULL.

Back in nfsd4_setattr(), the if (deleg_attrs) block then unconditionally
dereferences st->sc_type (at offset 4 from NULL), causing a kernel oops.

This is remotely triggerable by any NFSv4 client: send COMPOUND [PUTROOTFH,
SETATTR(ONE_STATEID, {bmval2=FATTR4_WORD2_TIME_DELEG_ACCESS, ...})].
No authentication, delegation, or prior state is required.

Fix by adding a NULL check before the dereference. A special stateid is
not a delegation stateid, so the existing nfserr_bad_stateid return value
is already correct; we only need to guard the pointer dereference itself.

## Which versions are affected by CVE-2026-89679?


## How do I fix CVE-2026-89679?

Apply the vendor's patch.

## Is CVE-2026-89679 being exploited?

There is no known exploitation of CVE-2026-89679 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89679 and fix it if it is affected.

What it is: CVE-2026-89679 is a high-severity 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-2026-89679 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-2026-89679/ (Markdown: https://insights.sbomify.com/CVE-2026-89679/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89679
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89679
- OSV: https://osv.dev/vulnerability/CVE-2026-89679

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89679/
Summaries are generated and may contain mistakes; the official description above is the record.