# CVE-2026-89696: nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref

> A remote attacker can cause a kernel crash in the Linux NFS server by sending a crafted COMPOUND request when inter-server copy is enabled.

- **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:** AZL-100671, BELL-CVE-2026-89696, DEBIAN-CVE-2026-89696, GHSA-78m3-prpr-8mjm, UBUNTU-CVE-2026-89696

## What is CVE-2026-89696?

CVE-2026-89696 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: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref

When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return
success with fh_dentry and fh_export both NULL if fh_verify() returns
nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag
is set, but the compound dispatch loop only uses this flag to bypass
the nfserr_nofilehandle check -- it does not prevent subsequent ops
from running with a NULL fh_dentry.

A remote client can exploit this by crafting a COMPOUND that includes
an inter-SSC COPY (which causes check_if_stalefh_allowed() to set
no_verify=true on the saved PUTFH) with an additional op inserted
between the source PUTFH and SAVEFH. For example, SETATTR calls
fh_want_write() which dereferences fh_export->ex_path.mnt without
calling fh_verify() first, causing a NULL pointer dereference in the
nfsd kthread.

Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set
and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow)
and ops with ALLOWED_WITHOUT_FH (which don't need a resolved
filehandle) may proceed. All other ops receive nfserr_stale, per
RFC 7862 Section 15.2.3 which specifies that foreign filehandle
validation is deferred to the consuming operation and NFS4ERR_STALE
returned at that point.

## Which versions are affected by CVE-2026-89696?


## How do I fix CVE-2026-89696?

Apply the vendor's patch.

## Is CVE-2026-89696 being exploited?

There is no known exploitation of CVE-2026-89696 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89696 and fix it if it is affected.

What it is: CVE-2026-89696 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-2026-89696 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-2026-89696/ (Markdown: https://insights.sbomify.com/CVE-2026-89696/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89696
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89696
- OSV: https://osv.dev/vulnerability/CVE-2026-89696

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89696/
Summaries are generated and may contain mistakes; the official description above is the record.