# CVE-2026-80921: KVM: s390: vsie: zero stale crypto bits

> A nested guest on s390x KVM can access stale crypto bits, potentially reading data from unavailable devices due to improper memory zeroing.

- **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:** 9 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-99950, BELL-CVE-2026-80921, DEBIAN-CVE-2026-80921, GHSA-337q-m32v-p95j, UBUNTU-CVE-2026-80921

## What is CVE-2026-80921?

CVE-2026-80921 is a high-severity vulnerability in Linux, published on 9 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: vsie: zero stale crypto bits

When shadowing crypto access bits from a format0 apcb (crycb 0 or 1),
the bits 64..255 are unchanged from whatever is in the vsie page in the
crycb and thus in the apcb. This gives a nested guest potential access
to a device no longer available. Zero out the remaining bits.

## Which versions are affected by CVE-2026-80921?


## How do I fix CVE-2026-80921?

Apply the vendor's patch.

## Is CVE-2026-80921 being exploited?

There is no known exploitation of CVE-2026-80921 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80921 and fix it if it is affected.

What it is: CVE-2026-80921 is a high-severity vulnerability in Linux, published on 9 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-2026-80921 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-2026-80921/ (Markdown: https://insights.sbomify.com/CVE-2026-80921/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80921
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80921
- OSV: https://osv.dev/vulnerability/CVE-2026-80921

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80921/
Summaries are generated and may contain mistakes; the official description above is the record.