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CVE-2026-64287
KVM: arm64: Bound used_lrs when flushing the pKVM hyp vCPU
Published 2026-07-25 (3 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-2026-64287 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 | fixedDSA-6405-1 · 2026-07-31 · text | 6.12.100-1 | Update the kernel and reboot. DSA-6405-1 shipped the fix on 2026-07-31, in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
flush_hyp_vcpu() copies the host vGIC state into the hyp's private vCPU on every run. The vGIC list register save and restore use used_lrs as their loop bound and expect it to stay within the number of implemented list registers. While this is generally the case, flush_hyp_vcpu() copies vgic_v3 verbatim and does not enforce this, so a value provided by the host is used at EL2 to index vgic_lr[] and access ICH_LR<n>_EL2 (host -> EL2). Fix by clamping used_lrs to the number of implemented list registers after the copy, as the trusted path already does in vgic_flush_lr_state(). The number of implemented list registers is constant after init, so it is replicated once from kvm_vgic_global_state.nr_lr into hyp_gicv3_nr_lr rather than read on every entry.
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/include/asm/kvm_hyp.h
arch/arm64/kvm/arm.c
arch/arm64/kvm/hyp/nvhe/hyp-main.c
- What this is
- KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)MAINTAINERS section matched on arch/arm64/include/asm/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.
- bookwormBnot built on arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- trixieBnot built on armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- forky, sidBnot built on armhf/armmp, armhf/armmp-lpae
- bookworm · linux-6.12Bnot built on armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- B
- built in on some, a module on others, absent on the rest
- 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
- 2026-07-25 (3 months ago)source
- CVSS
- 8.2 high
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.18%, higher than 6.5% 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 |
|---|---|---|
| 6.2 | 6.6.145 | 2c5e72b9fbf8 |
| 6.2 | 6.12.97 | 9fa301d82987 |
| 6.2 | 6.18.40 | c646431865f4 |
| 6.2 | 7.1.4 | 7fca3fcef81c |
| 6.2 | 7.2 | 8cc8bbbfab14 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DSA-6405-1 | 2026-07-31 | trixie 6.12.100-1 | tracker |
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
- A malicious or compromised arm64 EL1 host reaches the flaw through the local KVM vCPU-run hypercall into pKVM EL2. No network or adjacent protocol directly controls this internal field.
- AC:LAttack complexity, low
- On a pKVM/GICv3 system, the host can directly select an oversized used_lrs value and deterministically trigger the unchecked loops. No race or condition outside the attacker's control is required.
- PR:HPrivileges required, high
- Normal KVM paths keep used_lrs hardware-bounded, and neither an unprivileged KVM user nor a user namespace can assign it directly. Exploitation requires control of the host kernel at EL1, equivalent to real administrative privileges.
- UI:NUser interaction, none
- The malicious host can load and run a vCPU itself without any action by a protected-VM user or another victim.
- S:CScope, changed
- Exploitation crosses pKVM's EL1-host-to-EL2 isolation boundary and can affect hypervisor-private state and protected VMs outside the host's security authority.
- C:HConfidentiality impact, high
- The restore and synchronization paths can read beyond vgic_lr[] and transfer hyp-private vCPU data back into host-visible memory. EL2 compromise could expose protected-VM memory and other hypervisor secrets.
- I:HIntegrity impact, high
- The save path writes beyond vgic_lr[] into adjacent hyp-private vCPU metadata, including pointer, lock, and list state. This memory corruption is plausibly usable for EL2 control-flow hijacking and protected-VM modification.
- A:HAvailability impact, high
- Large bounds can cause extensive loops, invalid EL2 memory accesses, or corruption of critical hypervisor metadata. An nVHE hypervisor panic explicitly escalates to a host kernel panic.