Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources like networks, servers, storage, applications, and services that can be rapidly provisioned and released with minimal management effort or service provider interaction. Despite such promises, cloud computing has not been adopted at a pace that was expected. Among various reasons that prevent its widespread adoption, the most serious issue that Cloud Computing faces concerns its inability to insure data Confidentiality, Integrity, Availability, Authenticity and Privacy. Infrastructure as a service (IaaS) model serves as the underlying basis for other delivery model, and lack of security in this layer will certainly affect the other delivery models, i.e. PaaS and SaaS that are built upon IaaS layer. This paper provide the idea of infrastructure as a service models different security attributes which ensures the security in IaaS components and comparison of different IaaS vendors with respect to security attributes. Keywords—Cloud Computing, Cloud Security,