# CVE-2026-89955: s390/vfio-ap: Fix NULL deref in status_show() during queue probe

> A local attacker with access to s390/vfio-ap sysfs attributes can trigger a NULL pointer dereference, causing a kernel crash and denial of service.

- **Severity:** Not scored
- **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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101202, BELL-CVE-2026-89955, DEBIAN-CVE-2026-89955, GHSA-6vjc-f3pw-3x6w, UBUNTU-CVE-2026-89955

## What is CVE-2026-89955?

CVE-2026-89955 is a vulnerability in Linux, published on 16 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:

s390/vfio-ap: Fix NULL deref in status_show() during queue probe

When vfio_ap_mdev_probe_queue() creates the sysfs attribute group,
the queue's driver data has not yet been set. A concurrent read of
the 'status' attribute can therefore call dev_get_drvdata() and
get NULL, which is then passed directly to
vfio_ap_mdev_for_queue() where q->apqn is unconditionally
dereferenced, causing a NULL pointer dereference.

Fix this by acquiring the update locks before calling
sysfs_create_group(). The status_show() function acquires
guests_lock before reading the driver data, so any concurrent
read will block until after dev_set_drvdata() has been called
and the update locks are released.

As a bonus, the APQN no longer needs to be read from the queue
struct after allocation — it can be read directly from apdev
before allocation and stored in a local variable, which is then
assigned to q->apqn once the allocation succeeds.

## Which versions are affected by CVE-2026-89955?


## How do I fix CVE-2026-89955?

Apply the vendor's patch.

## Is CVE-2026-89955 being exploited?

There is no known exploitation of CVE-2026-89955 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89955 and fix it if it is affected.

What it is: CVE-2026-89955 is a vulnerability in Linux, published on 16 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-2026-89955 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-2026-89955/ (Markdown: https://insights.sbomify.com/CVE-2026-89955/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89955
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89955
- OSV: https://osv.dev/vulnerability/CVE-2026-89955

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89955/
Summaries are generated and may contain mistakes; the official description above is the record.