CVE-2026-98717

What the bug is

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.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

arch/x86/kvm/mmu/mmu.c

What this is

KERNEL VIRTUAL MACHINE FOR X86 (KVM/x86)MAINTAINERS section matched on arch/x86/kvm/*/ · kvm@vger.kernel.org · Supported

Show whether Debian builds this, per release

Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.

• bookworm, trixie, forky, sid?

?

not established - no Makefile entry for the affected file

Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS

Signals

Published

2026-10-18 (today)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

not scored

CISA KEV

not listedthe KEV catalogue

Debian urgency

unimportantsource

Subsystem

arch/x86

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
6.6	6.12.113	e1bcabc07efd
6.6	6.18.56	97c1dcce17ef
6.6	7.2.10	681e31f03ec9
6.6	7.3	b6249c1d5665