# CVE-2026-89691: nfsd: clear opcnt on compound arg release to prevent OOB read

> An out-of-bounds read in the Linux kernel NFS server allows leaking adjacent slab memory to userspace via netlink due to stale operation counts.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89691, DEBIAN-CVE-2026-89691, GHSA-v764-gh88-p9gg, UBUNTU-CVE-2026-89691

## What is CVE-2026-89691?

CVE-2026-89691 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: clear opcnt on compound arg release to prevent OOB read

nfsd4_release_compoundargs() resets args->ops to the inline iops[8]
array when the dynamically-allocated ops buffer is freed, but leaves
args->opcnt at its original value (which can be up to 200 for NFSv4.1+
compounds).

If rq_status_counter is stuck at an odd value (which can happen when
nfsd_dispatch() hits an error path after setting it odd), the RPC
status dumpit handler reads min(opcnt, 16) entries from args->ops[].
Since iops only has 8 elements and is the last field in struct
nfsd4_compoundargs, reading indices 8-15 accesses adjacent slab memory
and leaks it to userspace via netlink.

Zero opcnt unconditionally in nfsd4_release_compoundargs() so stale
compound metadata is never exposed through the status interface.

[ cel: Remove the kvfree_rcu_mightsleep() sleep from the exposure window ]

## Which versions are affected by CVE-2026-89691?


## How do I fix CVE-2026-89691?

Apply the vendor's patch.

## Is CVE-2026-89691 being exploited?

There is no known exploitation of CVE-2026-89691 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89691 and fix it if it is affected.

What it is: CVE-2026-89691 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89691 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-2026-89691/ (Markdown: https://insights.sbomify.com/CVE-2026-89691/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89691
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89691
- OSV: https://osv.dev/vulnerability/CVE-2026-89691

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89691/
Summaries are generated and may contain mistakes; the official description above is the record.