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CVE-2026-46317
KVM: arm64: Reassign nested_mmus array behind mmu_lock
Published 2026-06-09 (4 months ago) by the Linux kernel CNA. Subsystem arch/arm64. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-46317 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
kvm->arch.nested_mmus[] is walked under kvm->mmu_lock, including from the MMU notifier path (kvm_unmap_gfn_range() -> kvm_nested_s2_unmap()), which can run at any time. kvm_vcpu_init_nested() reallocates the array and frees the old buffer while holding only kvm->arch.config_lock, so such a walker can reference the freed array. Allocate the new array outside of mmu_lock, as the allocation can sleep. Under the lock, copy the existing entries, fix up the back pointers and reassign the array. Free the old buffer after dropping the lock, as kvfree() can sleep as well.
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/arm64/kvm/nested.c
- What this is
- KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)MAINTAINERS section matched on arch/arm64/kvm/ · linux-arm-kernel@lists.infradead.org · Maintained
- Kernel module
- kvm
Check it on the machine
grep -w CONFIG_KVM /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w kvmPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixieBnot built on armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- forky, sidBnot built on armhf/armmp, armhf/armmp-lpae
- ?
- not established - no Makefile entry for the affected file
- B
- built in on some, a module on others, absent on the rest
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.
- Build switch
- CONFIG_KVM
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 kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-06-09 (4 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.12%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- arch/arm64
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.11 | 6.18.35 | 918450ad6010 |
| 6.11 | 7.0.12 | 4424dbcb06d6 |
| 6.11 | 7.1 | 70543358fa08 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is reached only through KVM ioctls on /dev/kvm (KVM_CREATE_VCPU and KVM_ARM_VCPU_INIT), which drive kvm_vcpu_init_nested() while the MMU notifier path runs in the host kernel; this is a local syscall/ioctl attack surface, not a network protocol.
- AC:LAttack complexity, low
- Exploitation is a race between KVM_ARM_VCPU_INIT reallocating nested_mmus and MMU notifier unmaps, and the attacker controls both sides by concurrently creating/initializing vCPUs and manipulating guest memory regions to trigger kvm_unmap_gfn_range().
- PR:LPrivileges required, low
- The attacker needs access to /dev/kvm with nested virtualization enabled (KVM_ARM_VCPU_HAS_EL2), which a cloud tenant with nested-virt-capable AArch64 instances can obtain without host init-namespace root; this is not unauthenticated network access but is below full host administrator.
- UI:NUser interaction, none
- No victim interaction is required; the race can be driven entirely by the attacker's own KVM and memory-management ioctls from userspace.
- S:CScope, changed
- Successful exploitation corrupts host kernel memory from within a guest VM's KVM context, crossing the VM-to-hypervisor isolation boundary and enabling host kernel compromise (VM escape) on AArch64 cloud servers running nested virtualization.
- C:HConfidentiality impact, high
- The freed nested_mmus array is a use-after-free; concurrent walkers under mmu_lock dereference kvm_s2_mmu structures and their page-table pointers, enabling arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- UAF on kvm_s2_mmu objects that contain kvm_pgtable pointers and stage-2 page-table state can be leveraged for arbitrary kernel writes and control-flow hijacking, not merely a benign crash.
- A:HAvailability impact, high
- Concurrent access to the freed nested_mmus buffer during kvm_nested_s2_unmap() or related MMU walks can cause kernel oopses, panics, or hangs on the host.