CVE-2026-98717

Received Received - Intake

NULL Pointer Dereference in Linux Kernel KVM

Publication date: 2026-10-18

Last updated on: 2026-10-19

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Bail from shadow walks if the root is invalid or a dummy When walking shadow page tables, immediately terminate the walk if the root is a "dummy" root, i.e. a root whose top-level page table is backed by the zero page, but otherwise doesn't exist. If memslot creation races with a stage-2 page fault (EPT violation or #NPF) from L2, then if the stars align, KVM will attempt to walk shadow page tables using the zero page and hit a NULL pointer deref. BUG: kernel NULL pointer dereference, address: 0000000000000021 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP CPU: 30 UID: 1000 PID: 941 Comm: qemu Not tainted 7.2.0-rc2-1b731e5ded48-next-vm #1741 PREEMPTLAZY Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:__kvm_mmu_invalidate_addr+0xea/0x210 [kvm] Call Trace: <TASK> kvm_mmu_invalidate_addr+0x92/0xe0 [kvm] __kvm_inject_emulated_page_fault+0x67/0x80 [kvm] ept_page_fault+0x160/0x850 [kvm] kvm_mmu_do_page_fault+0x102/0x1f0 [kvm] kvm_mmu_page_fault+0x8e/0x6b0 [kvm] vmx_handle_exit+0x163/0x640 [kvm_intel] kvm_arch_vcpu_ioctl_run+0x960/0x2120 [kvm] kvm_vcpu_ioctl+0x2c7/0x970 [kvm] __x64_sys_ioctl+0x90/0xd0 do_syscall_64+0x67/0x5f0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f606d0b53bb Opportunistically harden the shadow walks against fully invalid roots, but WARN, as all callers are expected/required to pre-check for a valid root. Don't WARN in the dummy root case as the whole point of using a dummy root is to provide a root that's valid enough to enter the guest, i.e. it should Just Work for all flows except those that *need* to know about dummy roots. Alternatively, KVM could allocate a dedicated page and associated shadow page structure for the dummy root, which is very tempting as it such an approach should be more resilient against unexpected behavior. But that would be a much larger and thus riskier change than simply terminating walks of dummy roots.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-10-18

Last Modified

2026-10-19

Generated

2026-10-19

AI Q&A

2026-10-18

EPSS Evaluated

N/A

NVD

CVE-2026-98717

EUVD

EUVD-2026-103971

Affected Vendors & Products

Vendor	Product	Version / Range
Linux	Linux	0e3223d8d00ac05849661f1b8b476d3caca251cf
Linux	Linux	0e3223d8d00ac05849661f1b8b476d3caca251cf
Linux	Linux	0e3223d8d00ac05849661f1b8b476d3caca251cf
Linux	Linux	0e3223d8d00ac05849661f1b8b476d3caca251cf
Linux	Linux	6.6

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This is a Linux kernel vulnerability in the KVM (Kernel-based Virtual Machine) x86/mmu component. It occurs when shadow page table walks continue despite an invalid or dummy root page table. A race condition during memslot creation and stage-2 page faults (EPT violation or #NPF) can cause KVM to attempt walking shadow page tables using the zero page, leading to a NULL pointer dereference and kernel crash.

Detection Guidance

This vulnerability is specific to the Linux kernel's KVM (Kernel-based Virtual Machine) x86/mmu component. Detection requires checking for kernel NULL pointer dereference errors in KVM-related operations, particularly during shadow page table walks or EPT violations. Monitor kernel logs for Oops messages or NULL pointer dereference errors related to KVM modules.

Impact Analysis

This vulnerability can cause a denial of service by crashing the host system running virtual machines. If exploited, it may lead to unexpected system reboots or unresponsive hosts, disrupting services running on virtualized environments.

Compliance Impact

This vulnerability is a kernel NULL pointer dereference in KVM's shadow page table handling, which could lead to denial-of-service conditions in virtualized environments. It does not directly impact data confidentiality or integrity but may affect availability of systems processing sensitive data. Compliance impact would depend on whether the affected systems are used to process regulated data under GDPR or HIPAA.

Mitigation Strategies

Apply the latest kernel patches from your Linux distribution to resolve this issue. If patches are not yet available, consider disabling KVM virtualization temporarily until the fix is applied. Monitor vendor advisories for updates and test patches in a non-production environment before deployment.

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