Although more than eight years have passed since transient execution attacks such as Spectre and Meltdown shocked the computer industry, this class of vulnerabilities remains largely unexplored beyond well-studied targets such as the KVM hypervisor. Less mainstream, yet widely used, hypervisors have received comparatively little scrutiny from security researchers investigating transient execution attacks. While we often assume that our virtualization platform provides a secure and isolated environment for cloud workloads, malware analysis, and other untrusted software, that assumption does not always hold.

In this talk, we take a deep dive into transient execution attacks, with a particular focus on Branch Target Injection (BTI)-based Spectre attacks. After explaining the underlying exploitation techniques, we examine the mitigations implemented by modern hypervisors, using KVM as a reference point. We then turn our attention to FreeBSD's bhyve and Oracle VirtualBox and show that neither provides adequate protection against BTI attacks. To demonstrate the practical impact, we present end-to-end proof-of-concept exploits against both platforms that leak arbitrary memory from the host.