Bug 2536950 (CVE-2026-81627)

Summary:	CVE-2026-81627 qemu-kvm: VAPIC writable ROM alias can escape the option-ROM window and expose locked SMRAM
Product:	[Other] Security Response	Reporter:	Mauro Matteo Cascella <mcascell>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, eglynn, jdelft, jjoyce, jpretori, jschluet, jupierce, lgarciaa, lhh, mbiarnes, mburns, mgarciac, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
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Doc Text:	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.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2536972, 2536973
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Description Mauro Matteo Cascella 2026-09-18 09:53:45 UTC

A flaw was found in QEMU's VAPIC (Virtual Advanced Programmable Interrupt Controller) implementation in hw/i386/vapic.c. The 16-bit VAPIC setup hypercall allows a privileged guest to specify both the base address and size of a high-priority writable RAM alias. QEMU does not validate that this alias remains within the VAPIC option ROM boundaries (0xc0000..0xdffff). A malicious guest administrator can place the alias over 0xa0000..0xbffff, bypassing the Q35 chipset's D_LCK-protected SMRAM and modifying memory that executes in System Management Mode. This could allow a privileged guest user to inject arbitrary code into locked SMRAM.

Upstream fix: https://gitlab.com/qemu-project/qemu/-/commit/d61c8a6fb7388486353aa267ba0d75b098f16662

Reference: https://gitlab.com/qemu-project/qemu/-/work_items/4206