CVE-2025-40300

CVE-2025-40300, also known as VMSCAPE, is a Spectre-based vulnerability that affects AMD Zen CPUs (Zen 1 through Zen 5) and Intel Coffee Lake processors. It exploits incomplete branch predictor isolation in cloud environments, allowing a malicious guest user to potentially leak secrets from the hypervisor in the host domain. This attack is the first of its kind to enable a malicious guest VM to leak arbitrary memory from an unmodified hypervisor without requiring code modifications. The VMSCAPE attack targets the KVM/QEMU virtualization stack, demonstrating how attackers can extract cryptographic keys and other sensitive infrastructure secrets. Researchers have shown that VMSCAPE can leak memory data at a rate of 32 bytes per second, potentially extracting disk encryption keys in approximately 18 minutes on AMD Zen 4 processors. The vulnerability stems from the incomplete isolation of branch prediction state across virtualization boundaries, specifically between guest and host user processes. Linux kernel developers have released patches to mitigate VMSCAPE by adding an Indirect Branch Prediction Barrier (IBPB) on VMEXIT.