Cloud computing has transformed IT service delivery by offering scalable, on-demand resources over the internet. Among its service models—Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS)—PaaS provides a robust platform for developing, running, and managing applications without the complexity of maintaining the infrastructure. However, PaaS introduces a unique set of security concerns due to its multi-tenancy, abstraction layers, and reliance on third-party services. This paper explores the key security issues in PaaS environments, including data isolation, insecure APIs, platform vulnerabilities, insider threats, and compliance challenges. We also discuss mitigation strategies and emerging trends to enhance PaaS security.