VMScape: Academics Break Cloud Isolation With New Spectre Attack

VMScape is a Spectre-BTI based attack developed by academic researchers from ETH Zurich to break cloud isolation by leaking arbitrary memory from the host, including cryptographic keys, through the host–guest boundary. The PoC targets virtualization environments and can be used against AMD Zen CPUs and older Intel CPUs, exploiting incomplete branch predictor isolation despite mitigations.

Researchers report that VMScape can leak memory from the QEMU process at a rate of 32 bytes per second on AMD Zen 4, illustrating how secret data can be located and exfiltrated within about 1092 seconds. Patches addressing the issue have been rolled out for major Linux distributions under CVE-2025-40300, which carries a CVSS score of 6.5, and mitigations involve using an Indirect Branch Prediction Barrier before entering the hypervisor.

The findings were disclosed in June 2025, and the researchers note that the attack affects virtualized environments, with warnings that vulnerable hardware may exist in current cloud infrastructures, according to SecurityWeek.