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CVE-2026-64555
KVM: arm64: nv: Fix SPSR_EL2 restore in kvm_hyp_handle_mops()
Published 2026-07-27 (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-2026-64555 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 | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. 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
kvm_hyp_handle_mops() resets the single-step state machine as part of rewinding state for a MOPS exception by modifying vcpu_cpsr() and writing the result directly into hardware. In the case of nested virtualization, vcpu_cpsr() is a synthetic value such that the rest of KVM can deal with vEL2 cleanly. That means the value requires translation before being written into hardware, which is unfortunately missing from the MOPS handler. Fix it by directly modifying SPSR_EL2 and avoiding the synthetic state altogether, which will be resynchronized on the next 'full' exit back to KVM.
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/hyp/include/hyp/switch.h
- What this is
- KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)MAINTAINERS section matched on arch/arm64/kvm/ · linux-arm-kernel@lists.infradead.org · Maintained
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, bookworm · linux-6.12?
- ?
- 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
- 2026-07-27 (3 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
- 0.13%, higher than 2.2% 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 |
|---|---|---|
| 6.7 | 6.12.97 | 10a568010e82 |
| 6.7 | 6.18.40 | 884b44256041 |
| 6.7 | 7.1.5 | dd3b237eb778 |
| 6.7 | 7.2 | ff1022c3de46 |
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
- The attacker must be executing code inside a KVM/arm64 guest on the affected host — reached via /dev/kvm and guest instruction execution, not over any network protocol. This is local access to the host machine.
- AC:LAttack complexity, low
- A guest hypervisor at vEL2 triggers the MOPS exception at will by executing a main/epilogue MOPS instruction with ill-formed alignment/size parameters; there is no race and no dependence on CPU migration or single-step state, so corruption of hardware SPSR_EL2 is fully deterministic.
- PR:LPrivileges required, low
- Exploitation only needs the ability to create and run a nested-capable VM (/dev/kvm access, typically granted to unprivileged tenants/kvm-group users) and to run code inside that guest's own EL2 — no privilege on the host itself.
- UI:NUser interaction, none
- The guest triggers the faulty exception path entirely on its own during normal vCPU execution; no host user or administrator action is involved.
- S:CScope, changed
- The bogus ERET lands the guest's PC at real EL2 under the host's own EL2 translation regime and stack, with stage-2 no longer applied — the impact crosses the guest/host virtualization boundary into a different security authority.
- C:HConfidentiality impact, high
- Execution at EL2 with the host's TTBR0_EL2/TTBR1_EL2 active and guest-controlled registers gives read access to the entire host kernel address space and to other guests' memory.
- I:HIntegrity impact, high
- The guest obtains a controlled control-flow transfer into host kernel text at EL2 with all GPRs under its control, which is an arbitrary code execution / arbitrary write primitive against the host hypervisor.
- A:HAvailability impact, high
- Even without successful exploitation, ERETing to an unmapped or non-executable address at EL2 takes an unexpected EL2 exception that ends in a hyp panic, bringing down the host and every VM on it.