# CVE-2026-89957: s390/vfio-ap: Fix hot-unplug skipped when last AP adapter or domain removed

> A logic error in the Linux kernel vfio-ap driver allows KVM guests to retain stale access to unplugged AP devices, potentially exposing sensitive data.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101433, BELL-CVE-2026-89957, DEBIAN-CVE-2026-89957, GHSA-pgcj-5wj3-jcmr, UBUNTU-CVE-2026-89957

## What is CVE-2026-89957?

CVE-2026-89957 is a high-severity 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 hot-unplug skipped when last AP adapter or domain removed

The vfio_ap_mdev_hot_unplug_cfg() function uses the return value of
bitmap_andnot() to determine whether the guest APCB needs to be updated.
However, bitmap_andnot() returns false when the resulting destination
bitmap is empty. This means that if the only adapter, domain or control
domain assigned to an mdev is removed from the host's AP configuration,
the bit is correctly cleared from the shadow APCB, but bitmap_andnot()
returns false because the result is an empty bitmap. Consequently,
do_hotplug remains 0 and vfio_ap_mdev_update_guest_apcb() is never called,
leaving the KVM guest with stale hardware access to the unplugged AP
devices.

Fix this by replacing the bitmap_andnot() return value check with
bitmap_intersects() to determine whether the shadow APCB actually
overlaps with the removal mask. If there is an intersection, call
bitmap_andnot() solely for its side effect of clearing the bits, then
unconditionally set do_hotplug to trigger the guest APCB update.

## Which versions are affected by CVE-2026-89957?


## How do I fix CVE-2026-89957?

Apply the vendor's patch.

## Is CVE-2026-89957 being exploited?

There is no known exploitation of CVE-2026-89957 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89957 and fix it if it is affected.

What it is: CVE-2026-89957 is a high-severity 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-2026-89957 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-2026-89957/ (Markdown: https://insights.sbomify.com/CVE-2026-89957/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89957
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89957
- OSV: https://osv.dev/vulnerability/CVE-2026-89957

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89957/
Summaries are generated and may contain mistakes; the official description above is the record.