{"id":"CVE-2026-98717","title":"KVM: x86/mmu: Bail from shadow walks if the root is invalid or a dummy","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Bail from shadow walks if the root is invalid or a dummy\n\nWhen walking shadow page tables, immediately terminate the walk if the root\nis a \"dummy\" root, i…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < e1bcabc07efd029ab414894127411129ffdb8b48","Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < 97c1dcce17ef27853860c781f9912257e6adbf7c","Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < 681e31f03ec9219099a66a0f6e1bc48e1b5aa914","Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < b6249c1d5665098c8bf12f8d3e4712bf04c775bc","Linux 6.6"],"published":"2026-10-18","updated":"2026-10-18","sourceUpdated":"2026-10-18T15:46:51.862Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98717","references":[{"url":"https://git.kernel.org/stable/c/e1bcabc07efd029ab414894127411129ffdb8b48"},{"url":"https://git.kernel.org/stable/c/97c1dcce17ef27853860c781f9912257e6adbf7c"},{"url":"https://git.kernel.org/stable/c/681e31f03ec9219099a66a0f6e1bc48e1b5aa914"},{"url":"https://git.kernel.org/stable/c/b6249c1d5665098c8bf12f8d3e4712bf04c775bc"}],"tags":["cve.org"],"ingestedAt":"2026-10-18T16:47:32.510Z","slug":"CVE-2026-98717","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Bail from shadow walks if the root is invalid or a dummy\n\nWhen walking shadow page tables, immediately terminate the walk if the root\nis a \"dummy\" root, i.e. a root whose top-level page table is backed by the\nzero page, but otherwise doesn't exist.  If memslot creation races with a\nstage-2 page fault (EPT violation or #NPF) from L2, then if the stars align,\nKVM will attempt to walk shadow page tables using the zero page and hit a\nNULL pointer deref.\n\n  BUG: kernel NULL pointer dereference, address: 0000000000000021\n  #PF: supervisor read access in kernel mode\n  #PF: error_code(0x0000) - not-present page\n  PGD 0 P4D 0\n  Oops: Oops: 0000 [#1] SMP\n  CPU: 30 UID: 1000 PID: 941 Comm: qemu Not tainted 7.2.0-rc2-1b731e5ded48-next-vm #1741 PREEMPTLAZY\n  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n  RIP: 0010:__kvm_mmu_invalidate_addr+0xea/0x210 [kvm]\n  Call Trace:\n   <TASK>\n   kvm_mmu_invalidate_addr+0x92/0xe0 [kvm]\n   __kvm_inject_emulated_page_fault+0x67/0x80 [kvm]\n   ept_page_fault+0x160/0x850 [kvm]\n   kvm_mmu_do_page_fault+0x102/0x1f0 [kvm]\n   kvm_mmu_page_fault+0x8e/0x6b0 [kvm]\n   vmx_handle_exit+0x163/0x640 [kvm_intel]\n   kvm_arch_vcpu_ioctl_run+0x960/0x2120 [kvm]\n   kvm_vcpu_ioctl+0x2c7/0x970 [kvm]\n   __x64_sys_ioctl+0x90/0xd0\n   do_syscall_64+0x67/0x5f0\n   entry_SYSCALL_64_after_hwframe+0x4b/0x53\n  RIP: 0033:0x7f606d0b53bb\n\nOpportunistically harden the shadow walks against fully invalid roots, but\nWARN, as all callers are expected/required to pre-check for a valid root.\nDon't WARN in the dummy root case as the whole point of using a dummy root\nis to provide a root that's valid enough to enter the guest, i.e. it should\nJust Work for all flows except those that *need* to know about dummy roots.\n\nAlternatively, KVM could allocate a dedicated page and associated shadow\npage structure for the dummy root, which is very tempting as it such an\napproach should be more resilient against unexpected behavior.  But that\nwould be a much larger and thus riskier change than simply terminating\nwalks of dummy roots.\n\n## Affected\n\n- `Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < e1bcabc07efd029ab414894127411129ffdb8b48`\n- `Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < 97c1dcce17ef27853860c781f9912257e6adbf7c`\n- `Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < 681e31f03ec9219099a66a0f6e1bc48e1b5aa914`\n- `Linux >= 0e3223d8d00ac05849661f1b8b476d3caca251cf < b6249c1d5665098c8bf12f8d3e4712bf04c775bc`\n- `Linux 6.6`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}