# CVE-2026-89959: s390/vfio-ap: Fix control domain removal in vfio_ap_mdev_cfg_remove

> Incorrect bitmap operation in the Linux kernel s390 vfio-ap driver prevents proper removal of control domains from KVM guests.

- **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-101180, BELL-CVE-2026-89959, DEBIAN-CVE-2026-89959, GHSA-8mfq-hrvh-mwqh, UBUNTU-CVE-2026-89959

## What is CVE-2026-89959?

CVE-2026-89959 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 control domain removal in vfio_ap_mdev_cfg_remove

The vfio_ap_config_remove function uses the bitmap_andnot function to clear
bits from the matrix_mdev->matrix.adm bitmap (specifies the control domains
assigned to the mdev). This prevents the explicitly unplugged control
domains from being removed the KVM guest. The bitmap_and function is used
instead.

## Which versions are affected by CVE-2026-89959?


## How do I fix CVE-2026-89959?

Apply the vendor's patch.

## Is CVE-2026-89959 being exploited?

There is no known exploitation of CVE-2026-89959 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89959 and fix it if it is affected.

What it is: CVE-2026-89959 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-2026-89959 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-2026-89959/ (Markdown: https://insights.sbomify.com/CVE-2026-89959/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89959
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89959
- OSV: https://osv.dev/vulnerability/CVE-2026-89959

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89959/
Summaries are generated and may contain mistakes; the official description above is the record.