# CVE-2026-98638: KVM: arm64: Validate the SVE vector length in pkvm_vcpu_init_sve()

> A missing validation in KVM arm64 allows a privileged user to trigger a fatal kernel warning, causing a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-98638, DEBIAN-CVE-2026-98638, GHSA-jqwq-p3w6-jffx, UBUNTU-CVE-2026-98638

## What is CVE-2026-98638?

CVE-2026-98638 is a denial of service vulnerability in Linux, published on 18 Oct 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: arm64: Validate the SVE vector length in pkvm_vcpu_init_sve()

pkvm_vcpu_init_sve() clamps only the upper bound of the host-provided
sve_max_vl, so an invalid vector length reaches sve_state_size_from_vl()
and the WARN_ON() there, which is fatal at EL2. The existing
!sve_state_size test rejects such a length, but only after the macro has
run.

Check sve_vl_valid() before deriving the state size. A valid length
cannot yield a zero size, so the !sve_state_size test goes with it.

## Which versions are affected by CVE-2026-98638?


## How do I fix CVE-2026-98638?

Apply the vendor's patch.

## Is CVE-2026-98638 being exploited?

There is no known exploitation of CVE-2026-98638 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98638 and fix it if it is affected.

What it is: CVE-2026-98638 is a denial of service vulnerability in Linux, published on 18 Oct 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-2026-98638 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-2026-98638/ (Markdown: https://insights.sbomify.com/CVE-2026-98638/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98638
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98638
- OSV: https://osv.dev/vulnerability/CVE-2026-98638

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98638/
Summaries are generated and may contain mistakes; the official description above is the record.