Continuous Integration and Continuous Deployment (CI/CD) pipelines have become fundamental to modern software engineering, enabling rapid and reliable delivery of applications. However, their automation introduces critical vulnerabilities, particularly credential leaks and misconfigurations, which undermine the security of development and deployment environments. This study investigates security risks in Dock-er-based GitHub Actions workflows and proposes a tailored, DevSecOps-aligned security checklist to mitigate these threats. A systematic literature review was combined with hands-on experiments, in which controlled credential exposures and workflow misconfigurations were deliberately introduced and analyzed. Security controls such as secret scanning with GitGuardian and TruffleHog, configuration validation with GHAST, and access control enforcement were tested in a CI/CD testbed. The findings demonstrate that these integrated methods significantly reduce the risk of credential leakage and pipeline hijacking, while maintaining minimal performance overhead. The novelty of this work lies in consolidating fragmented best practices into a work-flow-specific model that is immediately applicable to real-world projects. This contrib-utes actionable guidance for secure-by-design CI/CD pipelines, offering practical protection against supply-chain threats while preserving delivery speed and scalability.