# CVE-2026-90103: NFSv4.2: fix LAYOUTSTATS send buffer exhaustion

> A malicious NFS server can cause a client-side kernel deadlock and denial of service by sending oversized LAYOUTSTATS responses that exhaust the send buffer.

- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102644, BELL-CVE-2026-90103, DEBIAN-CVE-2026-90103, GHSA-qgw9-h34w-h93j, UBUNTU-CVE-2026-90103

## What is CVE-2026-90103?

CVE-2026-90103 is a high-severity denial of service vulnerability in Linux, published on 17 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:

NFSv4.2: fix LAYOUTSTATS send buffer exhaustion

encode_layoutstats_maxsz budgets XDR_QUADLEN(PNFS_LAYOUTSTATS_MAXSIZE),
i.e. 256 bytes, for the layoutupdate4 body written by the layout driver.
The flexfiles record can exceed that.

ff_layout_encode_ff_layoutupdate() emits, per data server, a netaddr4,
an nfs_fh4, two ff_io_latency4, an nfstime4 and a bool.  A data server
whose filehandle is NFS_MAXFHSIZE bytes long already accounts for 132 of
those bytes, and the two ff_io_latency4 at 64 bytes each, the nfstime4
and the bool add a further 144, so the body passes 256 bytes before the
netaddr4 is encoded at all.  encode_layoutstats() additionally writes
the deviceid4 and the layoutupdate4 lou_type word, neither of which the
macro accounts for.

The filehandle and the address are both chosen by the server, through
LAYOUTGET and GETDEVICEINFO, so it can drive the encoder past the
end of the send buffer.  xdr_reserve_space() returns NULL once that
happens, and the two ff_layout_encode_io_latency() calls run with
dss_info->mirror->lock held, so a NULL return there leaves the lock
permanently held.

Raise PNFS_LAYOUTSTATS_MAXSIZE to 384 so that the record fits inside the
reservation.

## Which versions are affected by CVE-2026-90103?


## How do I fix CVE-2026-90103?

Apply the vendor's patch.

## Is CVE-2026-90103 being exploited?

There is no known exploitation of CVE-2026-90103 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90103 and fix it if it is affected.

What it is: CVE-2026-90103 is a high-severity denial of service vulnerability in Linux, published on 17 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-2026-90103 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-2026-90103/ (Markdown: https://insights.sbomify.com/CVE-2026-90103/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90103
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90103
- OSV: https://osv.dev/vulnerability/CVE-2026-90103

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90103/
Summaries are generated and may contain mistakes; the official description above is the record.