Cloud-Trust is a security assessment model for Infrastructure as a Service (IaaS) clouds that estimates high-level security metrics to quantify confidentiality and integrity. It assesses the security of four multi-tenant IaaS cloud architectures with different security controls. The probability of penetrating a cloud system (compromising high-value data) is high with minimal security controls, but drops substantially with a defense-in-depth architecture protecting VM images, strengthening access controls for administrators, and employing network security controls.