# CVE-2026-80859: fuse: fix missing barrier when checking io-uring readiness

> A missing memory barrier in the Linux kernel FUSE module can cause a race condition leading to a deadlock and denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-80859, DEBIAN-CVE-2026-80859, GHSA-66f3-f7p7-8q9g, UBUNTU-CVE-2026-80859

## What is CVE-2026-80859?

CVE-2026-80859 is a vulnerability in Linux, published on 4 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:

fuse: fix missing barrier when checking io-uring readiness

fuse_block_alloc() reads fch->initialized and then fch->io_uring.
fch->io_uring is set before fch->initialized, ordered by the smp_wmb()
in fuse_chan_set_intialized(), but fuse_block_alloc() has no matching
read barrier between the two loads.

This may lead a CPU to observe fch->initialized=1 but fch->io_uring=0,
and skip the check that blocks request allocation until the io-uring
queues are ready. This can reintroduce the lock-order inversion deadlock
that commit 3393ff964e0f prevents.

Add an smp_rmb() barrier to pair with the smp_wmb() in
fuse_chan_set_initialized() to prevent this.

## Which versions are affected by CVE-2026-80859?


## How do I fix CVE-2026-80859?

Apply the vendor's patch.

## Is CVE-2026-80859 being exploited?

There is no known exploitation of CVE-2026-80859 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80859 and fix it if it is affected.

What it is: CVE-2026-80859 is a vulnerability in Linux, published on 4 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-2026-80859 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-2026-80859/ (Markdown: https://insights.sbomify.com/CVE-2026-80859/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80859
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80859
- OSV: https://osv.dev/vulnerability/CVE-2026-80859

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80859/
Summaries are generated and may contain mistakes; the official description above is the record.