OWASP Kubernetes Security Cheat Sheet

Official docs outline

Securing Kubernetes Hosts
Host OS hardening and patching Kubernetes nodes.
Securing Kubernetes Components
Dashboard, etcd, API server, RBAC and kubelet protection.
Restricting Access to etcd
etcd authentication and encryption.
RBAC in Kubernetes
Least-privilege roles and bindings.
Build Phase Best Practices
Authorized images, CI scanning and minimal images.
Deploy Phase Best Practices
Namespaces, image policy and security contexts.
Security Context
Applying security contexts to pods and containers.
Network Policies
Restricting pod-to-pod traffic.
Runtime Phase Best Practices
Pod Security Admission, runtime monitoring and sandboxing.
Managed Kubernetes
Security responsibilities on cloud-managed clusters.
Supply Chain Security
Securing the container supply chain.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.