# CVE-2026-81627: Qemu-kvm: vapic writable rom alias can escape the option-rom window and expose locked smram

Status: published. Published: 2026-09-18. Updated: 2026-11-04.

A flaw was found in QEMU. The VAPIC setup hypercall in hw/i386/vapic.c does not validate that the writable RAM alias remains within the option ROM window. A privileged guest user on a Q35/KVM machine can position this alias over locked SMRAM, bypassing chipset D_LCK protection and injecting code into System Management Mode memory.

## Remediation

- workaround: The VAPIC TPR optimization can be disabled by preventing the kvmvapic option ROM from loading. When using libvirt, set the following in the guest's domain XML:
```
<features>
  <apic/>
  <hyperv>
    <vapic state='off'/>
  </hyperv>
</features>
```
When using QEMU directly, pass `-global kvmvapic.rom=off` on the command line.

This optimization is only used by 32-bit Windows guests for MMIO-based TPR register access. Linux guests, 64-bit Windows guests, and any guest using x2APIC or MSR-based TPR access are unaffected by disabling it. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (qemu-kvm): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (qemu-kvm): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (qemu-kvm): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (qemu-kvm-ma): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (virt-devel:rhel/qemu-kvm): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (virt:rhel/qemu-kvm): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (qemu-kvm): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux for NVIDIA 26 (qemu-kvm): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 5 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenStack Platform 13 (Queens) (qemu-kvm-rhev): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 8.2 (high); CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.19% as of 2026-11-04; percentile 8.93%

- SSVC: exploitation poc; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-787

## Exploit evidence

- exploit: https://gitlab.com/qemu-project/qemu/-/work_items/4206 (ADP: CISA-ADP)

## References

- https://access.redhat.com/security/cve/CVE-2026-81627 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2536950 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://gitlab.com/qemu-project/qemu/-/work_items/4206 (CNA: redhat)

- https://gitlab.com/qemu-project/qemu/-/work_items/4206 (ADP: CISA-ADP; exploit)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-81627; retrieved 2026-11-05; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-81627; retrieved 2026-11-05; source updated Not reported

Revision: 3d1c569a3c5c6778d54d47deea4361ac435b5673060ed164dce891edfe1ed83f

Canonical: https://y2.dev/cve/CVE-2026-81627

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