Infrastructure as a Service (IaaS) requires the greatest level of consumer responsibility for security. Managing Cloud documentation explains that in the shared responsibility model, IaaS providers supply virtualized infrastructure components such as compute, storage, and networking, while consumers manage everything above that layer.

Customers are responsible for securing operating systems, applications, data, access controls, patching, and configuration management. This includes vulnerability management, endpoint security, identity management, and monitoring. While this model provides flexibility and control, it also demands strong security expertise and governance.

In contrast, PaaS and SaaS shift more security responsibilities to the provider, and DBaaS abstracts database management. Therefore, IaaS places the highest security responsibility on the consumer.