CVE-2026-64561
Received Received - Intake

KVM x86 Shadow MMU Invalid Root Handling Flaw

Publication date: 2026-08-04

Last updated on: 2026-08-04

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Check for invalid/obsolete root *after* making MMU pages available Check for a "stale" page fault, i.e. for an invalid and/or obsolete root, after making MMU pages available for the shadow MMU. If reclaiming shadow pages zaps an in-use root, i.e. marks it invalid, then KVM will attempt to map memory into an invalid root. On its own, populating an invalid root is "fine", but because child shadow pages inherit their parent's role, any children created during the map/fetch will be created as invalid pages, thus violating KVM's invariant that invalid pages are never on the list of active MMU pages. Note, the underlying flaw has existed since KVM first started tracking invalid roots in 2008 (commit 2e53d63acba7, "KVM: MMU: ignore zapped root pagetables"), but the true badness only came along in 2020 (Linux 5.9) with the invariant that invalid shadow pages can't be on the list of active pages. Note #2, inheriting role.invalid when creating child shadow pages is also far from ideal; that flaw will be addressed separately.

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Meta Information

Published
2026-08-04
Last Modified
2026-08-04
Generated
2026-08-04
AI Q&A
2026-08-04
EPSS Evaluated
N/A
NVD
CVE-2026-64561
EUVD
EUVD-2026-52602

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel From 5.9 (inc)

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a Linux kernel vulnerability in KVM (Kernel-based Virtual Machine) for x86 systems. It involves a race condition where invalid or obsolete memory management unit (MMU) roots are checked after making shadow MMU pages available. This can lead to invalid shadow pages being added to the active MMU page list, violating KVM's invariant that invalid pages should never be active.

Detection Guidance

This vulnerability is specific to the Linux kernel's KVM (Kernel-based Virtual Machine) x86 component. Detection requires checking the kernel version and KVM module behavior. Use commands like 'uname -a' to check the kernel version and 'lsmod | grep kvm' to verify KVM module status. Look for kernel logs with 'dmesg | grep -i kvm' for errors related to invalid root page faults.

Impact Analysis

This vulnerability could allow a guest virtual machine to cause a denial of service (DoS) or potentially execute arbitrary code in the host kernel. It may lead to system instability, crashes, or unauthorized access if exploited by an attacker with local guest access.

Mitigation Strategies

Update the Linux kernel to a patched version that resolves this issue. Check your distribution's security advisories for kernel updates. If using a vulnerable kernel, avoid running virtual machines with KVM until patched. Monitor kernel logs for KVM-related errors as a sign of exploitation.

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