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CVE-2026-74516
KVM: SVM: Update x2APIC MSR intercepts if AVIC is inhibited while L2 is active
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem arch/x86. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74516 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Always update x2APIC MSR intercepts for L1 when AVIC is deactivated, even if L2 is active and KVM is using a separate MSR bitmap to run L2. If AVIC is fully enabled prior to running L2, and is then inhibited while L2 is active (for a VM-scoped inhibit), then KVM will run L1 with AVIC disabled, but with x2APIC MSR intercepts disabled, i.e. will allow L1 to read most of the host's APIC state, send arbitrary interrupts, change task priority, and ultimately trivially DoS the host. E.g. sending a self-IPI in L1 on HYPERV_REENLIGHTENMENT_VECTOR, 0xee, with CONFIG_HYPERV=n in the host kernel as a "safe" PoC, yields: Spurious interrupt (vector 0xee) on CPU#425. Acked And hacking KVM to abuse kvm_set_posted_intr_wakeup_handler() to register a handler and WARN on POSTED_INTR_WAKEUP_VECTOR yields: ------------[ cut here ]------------ WARNING: arch/x86/kvm/svm/svm.c:5594 at pi_wakeup_handler+0x9/0x10 [kvm_amd], CPU#156: nested_x2apic_t/316940 CPU: 156 UID: 0 PID: 316940 Comm: nested_x2apic_t Tainted: G S U Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER Hardware name: Google Astoria-Turin/astoria, BIOS 0.20260209.0-0 02/09/2026 RIP: 0010:pi_wakeup_handler+0x9/0x10 [kvm_amd] Call Trace: <IRQ> sysvec_kvm_posted_intr_wakeup_ipi+0x64/0x80 </IRQ> <TASK> asm_sysvec_kvm_posted_intr_wakeup_ipi+0x1a/0x20 RIP: 0010:vcpu_run+0x1430/0x1e40 [kvm] kvm_arch_vcpu_ioctl_run+0x2c1/0x600 [kvm] kvm_vcpu_ioctl+0x580/0x6b0 [kvm] __se_sys_ioctl+0x6d/0xb0 do_syscall_64+0x10a/0x480 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x46ff4b </TASK> ---[ end trace 0000000000000000 ]---
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/x86/kvm/svm/avic.c
- What this is
- KERNEL VIRTUAL MACHINE FOR X86 (KVM/x86)MAINTAINERS section matched on arch/x86/kvm/*/ · kvm@vger.kernel.org · Supported
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
- 2026-08-15 (2 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
- 0.14%, higher than 2.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- arch/x86
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.0 | 6.1.183 | 4ca05385b3dd |
| 6.0 | 6.6.151 | 6664a5aea453 |
| 6.0 | 6.12.103 | f12373625b4d |
| 6.0 | 6.18.44 | 7668c58dcf46 |
| 6.0 | 7.1.8 | 89f9e8398e79 |
| 6.0 | 7.2 | 7d3aae206663 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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
- Exploitation requires triggering KVM nested SVM/AVIC paths via local /dev/kvm ioctls (KVM_CREATE_VM, KVM_CREATE_VCPU, KVM_RUN) from L1; there is no network, adjacent, or physical packet/device path to the vulnerable code.
- AC:LAttack complexity, low
- An L1 attacker fully controls nested VM configuration (x2APIC, AVIC, L2 MSR bitmap, IRQ-window/ExtINT conditions) and can reliably reproduce AVIC inhibition while L2 is active without races or uncontrollable host state.
- PR:HPrivileges required, high
- Reaching the bug requires running nested AMD KVM as L1 (nested virtualization enabled and control of a guest hypervisor), which is not available to an unprivileged host user or via user-namespace capabilities alone without delegated /dev/kvm access.
- UI:NUser interaction, none
- No victim interaction is required; exploitation is driven entirely by the attacker’s nested hypervisor configuration and KVM_RUN operations once nested virtualization is available.
- S:CScope, changed
- The flaw lets an L1 nested guest hypervisor access the host’s physical x2APIC MSRs, crossing the VM/host security boundary rather than staying within the guest’s own security scope.
- C:HConfidentiality impact, high
- With x2APIC MSR intercepts left disabled, L1 can read most of the host APIC state (IDs, IRR/ISR, timers, ICR), leaking sensitive host interrupt-controller information beyond the guest boundary.
- I:HIntegrity impact, high
- L1 can write host x2APIC MSRs to send arbitrary IPIs, change task priority, and invoke host interrupt vectors (e.g. posted-interrupt wakeup), enabling host integrity compromise beyond mere guest-local effects.
- A:HAvailability impact, high
- Host availability is trivially impacted by injecting spurious or high-priority interrupts to host CPUs; the fix commit demonstrates host kernel warnings and spurious interrupt storms causing denial of service.