High [CVE-2026-81627] Qemu-kvm: vapic writable rom alias can escape the option-rom window and expose locked smram
This high-severity Red Hat Linux advisory covers CVE-2026-81627 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8.
Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.
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Summary
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. This flaw allows a privileged guest to bypass SMRAM locking on Q35 machine types by placing the VAPIC writable ROM alias outside the option-ROM window.
While the kvmvapic TPR optimization is normally used only by 32-bit Windows guests, any privileged guest can deliberately invoke the VAPIC setup hypercall to trigger the vulnerable code path. Exploitation requires guest root access and KVM acceleration.
Red Hat severity: Important — CVSS 8.2 (CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H). Weakness: CWE-787.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat Enterprise Linux for NVIDIA 26; Red Hat OpenShift Container Platform 4; Red Hat OpenStack Platform 13 (Queens). Red Hat lists Red Hat Enterprise Linux 6 as not affected.
Will not fix / out of support: Red Hat Enterprise Linux for NVIDIA 26; Red Hat OpenStack Platform 13 (Queens). Red Hat does not currently list a fixing RHSA for this CVE.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 11 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 11 days ago·verify at source
Mitigation checklist
- 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.
Official advisory · high-confidence parse· fetched 11 days ago·verify at source
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