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Fencer Vulns
high 8.8

CVE-2026-63807 json

KVM: x86/mmu: Ensure hugepage is in by slot before checking max mapping level

published 2026-07-19 3 mo ago modified 2026-10-19 20 d ago also EUVD-2026-45473

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86/mmu: Ensure hugepage is in by slot before checking max mapping level

When recovering hugepages in the shadow MMU, verify that the base gfn of the shadow page is actually contained within the target memslot, *before* querying the max mapping level given the shadow page's gfn. Failure to pre-check the validity of the gfn can lead to an out-of-bounds access to the slot's lpage_info (which typically manifests as a host #PF because the lpage_info is vmalloc'd) if the guest creates a hugepage mapping (in its PTEs) that extends "below" the bounds of a memslot.

When faulting in memory for a guest, and the size of the guest mapping is greater than KVM's (current) max mapping, then KVM will create a "direct" shadow page (direct in that there are no gPTEs to shadow, and so the target gfn is a direct calculation given the base gfn of the shadow page). The hugepage recovery flow looks for such direct shadow pages, as forcing 4KiB mappings when dirty logging generates the guest > host mapping size case. When the 4KiB restriction is lifted, then KVM can replace the shadow page with a hugepage.

But if KVM originally used a smaller mapping than the guest because the range of memory covered by the guest hugepage exceeds the bounds of a memslot, then KVM will link a direct shadow page with a gfn that is outside the bounds of the memslot being used to fault in memory. The rmap entry added for the leaf mapping is correct and within bounds, but the gfn of the leaf SPTE's parent shadow page will be out of bounds.

BUG: unable to handle page fault for address: ffffc90000806ffc #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 100000067 P4D 100000067 PUD 1002a7067 PMD 10612f067 PTE 0 Oops: Oops: 0000 [#1] SMP CPU: 13 UID: 1000 PID: 757 Comm: mmu_stress_test Not tainted 7.1.0-rc1-48ce1e26eace-x86_pir_to_irr_comments-vm #341 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:kvm_mmu_max_mapping_level+0x79/0x2b0 [kvm] Call Trace: <TASK> kvm_mmu_recover_huge_pages+0x21b/0x320 [kvm] kvm_set_memslot+0x1ee/0x590 [kvm] kvm_set_memory_region.part.0+0x3a1/0x4d0 [kvm] kvm_vm_ioctl+0x9bf/0x15d0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb7/0xbb0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f21c0f1a9bf </TASK>

Don't bother pre-checking the bounds of the potential hugepage, i.e. don't check that e.g. sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level + 1) is also within the memslot, as the checks performed by kvm_mmu_max_mapping_level() are a superset of the basic bounds checks. I.e. pre-checking the full range would be a dubious micro-optimization.

Patch / fix

  • Linux Linux 5.15.211, 6.1.177, 6.6.144, 6.12.95, 6.18.38, 7.1.3, 7.2
  • linux Debian 12 6.1.177-1
  • linux Debian 13 6.12.95-1
  • linux Debian 14 7.1.3-1

debian advisories DEBIAN-CVE-2026-63807

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-147.147
  • linux Ubuntu 26.04 LTS 7.0.0-31.31
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1067.70
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1012.12
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1071.79

ubuntu advisories UBUNTU-CVE-2026-63807

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel enterprise linux eus 10.0 6.12.0-55.94.1.el10_0
  • rv enterprise linux eus 10.0 6.12.0-55.94.1.el10_0
  • perf enterprise linux eus 10.0 6.12.0-55.94.1.el10_0
  • rtla enterprise linux eus 10.0 6.12.0-55.94.1.el10_0
  • libperf enterprise linux eus 10.0 6.12.0-55.94.1.el10_0
  • kernel-rt enterprise linux eus 10.0 6.12.0-55.94.1.el10_0
  • kernel-64k enterprise linux eus 10.0 6.12.0-55.94.1.el10_0
  • kernel-core enterprise linux eus 10.0 6.12.0-55.94.1.el10_0

red hat advisories RHSA-2026:49030

  • kernel-default SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Live Patching 15 SP6 +1 more 6.4.0-150600.23.130.1
  • kernel-64kb SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS, SLE High Performance Computing 15 SP5-ESPOS 5.14.21-150500.55.182.1
  • kernel-syms SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.182.1
  • kernel-source SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.182.1
  • kernel-default SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +3 more 5.14.21-150500.55.182.1
  • kernel-obs-build SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.182.1
  • kernel-default-base SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.182.1.150500.6.85.2
  • kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.72.1

suse advisories SUSE-SU-2026:3602-1SUSE-SU-2026:3595-1SUSE-SU-2026:3810-1SUSE-SU-2026:3790-1SUSE-SU-2026:23244-1SUSE-SU-2026:23241-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.37.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.37.1

opensuse advisories openSUSE-SU-2026:21555-1openSUSE-SU-2026:11339-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-63807 updated cvss 7.0

kernel: KVM: x86/mmu: Ensure hugepage is in by slot before checking max mapping level

  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    affected: no fix available
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) rv 6.12.0-55.94.1.el10_0, perf 6.12.0-55.94.1.el10_0, rtla 6.12.0-55.94.1.el10_0, python3-perf 6.12.0-55.94.1.el10_0, kernel-devel-matched 6.12.0-55.94.1.el10_0, kernel-64k-devel-matched 6.12.0-55.94.1.el10_0, +7 more Red Hat Enterprise Linux BaseOS EUS (v. 10.0) kernel 6.12.0-55.94.1.el10_0, kernel-64k 6.12.0-55.94.1.el10_0, kernel-core 6.12.0-55.94.1.el10_0, kernel-tools 6.12.0-55.94.1.el10_0, kernel-modules 6.12.0-55.94.1.el10_0, kernel-64k-core 6.12.0-55.94.1.el10_0, +27 more Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) libperf 6.12.0-55.94.1.el10_0, kernel-debuginfo-common-s390x 6.12.0-55.94.1.el10_0, kernel-debuginfo-common-x86_64 6.12.0-55.94.1.el10_0, kernel-debuginfo-common-aarch64 6.12.0-55.94.1.el10_0, kernel-debuginfo-common-ppc64le 6.12.0-55.94.1.el10_0 Red Hat Enterprise Linux Real Time EUS (v. 10.0) kernel-rt 6.12.0-55.94.1.el10_0, kernel-rt-64k 6.12.0-55.94.1.el10_0, kernel-rt-core 6.12.0-55.94.1.el10_0, kernel-rt-modules 6.12.0-55.94.1.el10_0, kernel-rt-64k-core 6.12.0-55.94.1.el10_0, kernel-rt-debug-core 6.12.0-55.94.1.el10_0, +14 more Red Hat Enterprise Linux Real Time for NFV EUS (v. 10.0) kernel-rt 6.12.0-55.94.1.el10_0, kernel-rt-kvm 6.12.0-55.94.1.el10_0, kernel-rt-core 6.12.0-55.94.1.el10_0, kernel-rt-modules 6.12.0-55.94.1.el10_0, kernel-rt-debug-kvm 6.12.0-55.94.1.el10_0, kernel-rt-debug-core 6.12.0-55.94.1.el10_0, +6 more
    fixed: vendor fix RHSA-2026:49030
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.