# CVE-2026-89921: KVM: s390: Zero initialize data structures for inject_pfault_token

> A local attacker with KVM access can read uninitialized kernel stack memory via migration ioctls due to missing zero-initialization in s390 fault injection.

- **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:** 21 Oct 2026
- **Also known as:** AZL-101535, BELL-CVE-2026-89921, DEBIAN-CVE-2026-89921, GHSA-fm87-69w9-6w3j, UBUNTU-CVE-2026-89921

## What is CVE-2026-89921?

CVE-2026-89921 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:

KVM: s390: Zero initialize data structures for inject_pfault_token

__kvm_inject_pfault_token() only sets .type and .u.ext.ext_params2 of
the on-stack struct kvm_s390_irq but the full ext substructure is copied
into the cpu local variable on inject. ext_params and pad contain stale
stack values.

Interrupt delivery only uses ext_params2, so nothing leaks to the guest,
but a host user can use the migration ioctls to get to the data.

Fix by zero-initializing the irq struct.
Do the same for the inti data structure.

## Which versions are affected by CVE-2026-89921?


## How do I fix CVE-2026-89921?

Apply the vendor's patch.

## Is CVE-2026-89921 being exploited?

There is no known exploitation of CVE-2026-89921 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89921 and fix it if it is affected.

What it is: CVE-2026-89921 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-2026-89921 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-2026-89921/ (Markdown: https://insights.sbomify.com/CVE-2026-89921/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89921
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89921
- OSV: https://osv.dev/vulnerability/CVE-2026-89921

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89921/
Summaries are generated and may contain mistakes; the official description above is the record.