# CVE-2026-74516: KVM: SVM: Update x2APIC MSR intercepts if AVIC is inhibited while L2 is active

> A guest VM can escalate privileges and cause host denial of service by reading APIC state and sending interrupts when AVIC is inhibited during nested virtualization.

- **Severity:** High 8.2 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-96150, BELL-CVE-2026-74516, DEBIAN-CVE-2026-74516, GHSA-p473-wqx8-95rq, UBUNTU-CVE-2026-74516

## What is CVE-2026-74516?

CVE-2026-74516 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

KVM: SVM: Update x2APIC MSR intercepts if AVIC is inhibited while L2 is active

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 ]---

## Which versions are affected by CVE-2026-74516?


## How do I fix CVE-2026-74516?

Apply the vendor's patch.

## Is CVE-2026-74516 being exploited?

There is no known exploitation of CVE-2026-74516 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74516 and fix it if it is affected.

What it is: CVE-2026-74516 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74516 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74516/ (Markdown: https://insights.sbomify.com/CVE-2026-74516/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74516
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74516
- OSV: https://osv.dev/vulnerability/CVE-2026-74516

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74516/
Summaries are generated and may contain mistakes; the official description above is the record.