# CVE-2026-89674: nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget

> A flaw in the Linux kernel NFS server allows out-of-bounds writes or memory leaks, potentially enabling code execution or data disclosure.

- **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:** 19 Oct 2026
- **Also known as:** AZL-100637, BELL-CVE-2026-89674, DEBIAN-CVE-2026-89674, GHSA-qhmp-vm7x-v422, UBUNTU-CVE-2026-89674

## What is CVE-2026-89674?

CVE-2026-89674 is a critical memory corruption 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 XDR length calculation in nfsd4_ff_encode_layoutget

The XDR buffer size calculation in nfsd4_ff_encode_layoutget() has
multiple errors that can result in either an out-of-bounds write or
leaking uninitialized kernel memory to the client:

 - fh_len doesn't account for XDR padding on the file handle data
 - uid and gid lengths use "8 + len" but xdr_encode_opaque() actually
   writes "4 + xdr_align_size(len)" bytes
 - ds_len omits the flags and stats_collect_hint fields (8 bytes),
   while len's header constant overestimates by 8 bytes -- these
   partially cancel but leave a net mismatch

The worst case occurs with short strings (e.g. uid=0, gid=0 with an
odd-sized file handle), where the function writes up to 5 bytes past
the reserved XDR buffer. Conversely, when string lengths happen to be
4-byte aligned, the reservation is too large and stale buffer content
is sent to the client.

Fix this by breaking out every encoded field explicitly in the ds_len
calculation, using xdr_align_size() for all variable-length opaque
fields, and correcting the header constants.

## Which versions are affected by CVE-2026-89674?


## How do I fix CVE-2026-89674?

Apply the vendor's patch.

## Is CVE-2026-89674 being exploited?

There is no known exploitation of CVE-2026-89674 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89674 and fix it if it is affected.

What it is: CVE-2026-89674 is a critical memory corruption 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-2026-89674 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-2026-89674/ (Markdown: https://insights.sbomify.com/CVE-2026-89674/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89674
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89674
- OSV: https://osv.dev/vulnerability/CVE-2026-89674

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89674/
Summaries are generated and may contain mistakes; the official description above is the record.