Bug 2555141 (CVE-2026-98720)

Summary: CVE-2026-98720 kernel: KVM: nVMX: Force MSR bitmap refresh if runtime eVMCS controls are modified
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's KVM (Kernel-based Virtual Machine) nested virtualization implementation. This flaw allows an attacker within a nested guest to bypass isolation boundaries and directly access host hardware controls, potentially causing host system instability or a Denial of Service (DoS). The issue occurs when nested virtualization control settings are modified without refreshing internal register permissions, leaving the host's Task Priority Register (TPR) directly accessible to the guest.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-10-18 15:56:45 UTC 
In the Linux kernel, the following vulnerability has been resolved:

KVM: nVMX: Force MSR bitmap refresh if runtime eVMCS controls are modified

Force a refresh of the vmcs02 MSR bitmap during nested VM-Enter if the
runtime eVMCS controls (pin, primary, secondary, etc.) are being updated.
If L1 isn't intercepting TPR writes, runs L2 with TPR virtualization, and
then runs the same L2 with TPR virtualization disabled, KVM will fail to
refresh msr_bitmap02 and leave TPR in passthrough mode even though TPR
virtualization is disabled.  I.e. failure to refresh the bitmap lets L2 (or
L1 by proxy) read and write L0's TPR.
Comment 1 Mauro Matteo Cascella 2026-10-22 17:22:29 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98720.mbox