Trail of Atredis (Trail of Bits and Atredis Partners) have released findings on Kubernetes security in a series of GitHub documents

Overall, Kubernetes is a large system with significant operational complexity. The assessment team found configuration and deployment of Kubernetes to be non-trivial, with certain components having confusing default settings, missing operational controls, and implicitly defined security controls. The codebase is large and complex, with large sections of code containing minimal documentation and numerous dependencies, including systems external to Kubernetes.