# CVE-2026-89920: KVM: s390: Fix memory corruption by not reinjecting CK machine checks

> A memory corruption vulnerability in the Linux kernel's KVM s390 subsystem allows attackers to potentially execute code or escalate privileges via improper machine check handling.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:H/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:** 21 Oct 2026
- **Also known as:** AZL-101664, BELL-CVE-2026-89920, DEBIAN-CVE-2026-89920, GHSA-vhrh-h65f-3j9h, UBUNTU-CVE-2026-89920

## What is CVE-2026-89920?

CVE-2026-89920 is a high-severity memory corruption 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:

KVM: s390: Fix memory corruption by not reinjecting CK machine checks

Channel-subsystem damage machine checks are for the host channel
subsystem. The guest channel subsystem is emulated in the userspace VMM.
There is no point in forwarding such machine checks into the guest.

This also simplifies the machine check reinjection and avoids kfree of a
stack variable as reported by sashiko.  There might be still machine
checks that have the ck bit set with another bit (like instruction
damage), mask out the CK bit in s390_backup_mcck_info(), like the CP and
ED bits already are.

## Which versions are affected by CVE-2026-89920?


## How do I fix CVE-2026-89920?

Apply the vendor's patch.

## Is CVE-2026-89920 being exploited?

There is no known exploitation of CVE-2026-89920 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89920 and fix it if it is affected.

What it is: CVE-2026-89920 is a high-severity memory corruption 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-2026-89920 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-2026-89920/ (Markdown: https://insights.sbomify.com/CVE-2026-89920/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89920
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89920
- OSV: https://osv.dev/vulnerability/CVE-2026-89920

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89920/
Summaries are generated and may contain mistakes; the official description above is the record.