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VMScape attack breaks guest-host isolation on AMD, Intel CPUs

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A new speculative execution attack named VMScape allows malicious virtual machines (VMs) to leak cryptographic keys from an unmodified QEMU hypervisor process running on modern AMD or Intel CPUs. The attack bypasses existing Spectre mitigations and threatens to leak sensitive data by leveraging speculative execution. It affects all AMD Zen 1 to Zen 5 processors and Intel’s Coffee Lake CPUs, but not Raptor Cove or Gracemont. The attack does not require compromising the host and works on unmodified virtualization software with default mitigations enabled on the hardware. The VMScape attack targets QEMU, the user-mode hypervisor component, by influencing indirect branch prediction in a host user process due to shared Branch Prediction Unit (BPU) structures. The attack uses a Spectre-BTI (Branch Target Injection) technique to misguide a target indirect branch in QEMU, enabling the leakage of secret data. The ETH Zurich research team reported the findings to AMD and Intel, who have released patches and security bulletins. Linux kernel developers have also released patches to mitigate the issue.

Timeline

  1. 11.09.2025 18:05 1 articles · 21d ago

    VMScape attack breaks guest-host isolation on AMD, Intel CPUs

    A new speculative execution attack named VMScape allows malicious virtual machines (VMs) to leak cryptographic keys from an unmodified QEMU hypervisor process running on modern AMD or Intel CPUs. The attack bypasses existing Spectre mitigations and threatens to leak sensitive data by leveraging speculative execution. The attack affects all AMD Zen 1 to Zen 5 processors and Intel’s Coffee Lake CPUs, but not Raptor Cove or Gracemont. The ETH Zurich research team reported the findings to AMD and Intel, who have released patches and security bulletins. Linux kernel developers have also released patches to mitigate the issue.

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