# CVE-2026-89916: KVM: arm64: Make VNCR invalidation participate in MMU invalidation retry

> A race condition in KVM arm64 VNCR invalidation allows attackers to execute arbitrary code or escalate privileges within the guest.

- **Severity:** Critical 9.3 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **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:** BELL-CVE-2026-89916, DEBIAN-CVE-2026-89916, GHSA-5p99-rg43-px7f, UBUNTU-CVE-2026-89916

## What is CVE-2026-89916?

CVE-2026-89916 is a critical 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: arm64: Make VNCR invalidation participate in MMU invalidation retry

A VNCR TLB invalidation can occur on one vcpu while another vcpu is
faulting in this same page. Without correctly handling this, we can
end up with the following scenario:

- vcpu A walks the PTs to translate VNCR
- before vcpu A is able to grab the MMU lock to insert the TLB,
  vcpu B updates the S1 PTs with an invalid entry, and issues
  a TLBI S1E2 for this VA
- vcpu A inserts the TLB for something that is now invalid

This isn't a new problem, and we manage S2 by having the MMU notifier
to bump up mmu_invalidate_seq on invalidation so that the fault can be
replayed.

We can perform something similar here, and extend invalidate_vncr_va() to
update the same counter, clearly indicating that the context has
changed under our feet. This is safe as the invalidation always happen
while holding the MMU lock for write, and that we sample the sequence
number before walking S1.

## Which versions are affected by CVE-2026-89916?


## How do I fix CVE-2026-89916?

Apply the vendor's patch.

## Is CVE-2026-89916 being exploited?

There is no known exploitation of CVE-2026-89916 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89916 and fix it if it is affected.

What it is: CVE-2026-89916 is a critical 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-2026-89916 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-2026-89916/ (Markdown: https://insights.sbomify.com/CVE-2026-89916/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89916
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89916
- OSV: https://osv.dev/vulnerability/CVE-2026-89916

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89916/
Summaries are generated and may contain mistakes; the official description above is the record.