Kubernetes YAML is a declarative manifest format used to describe the desired state of objects in a Kubernetes cluster. Instead of issuing step-by-step commands, an operator writes YAML that says what should exist, such as deployments, roles, services, or custom resources. The control plane then tries to make the cluster match that file.
In security terms, YAML matters because it is often the entry point for automation. A manifest can create workloads, change permissions, or trigger controllers that act on external systems. If a controller has broader privileges than the person submitting the file, the YAML becomes a request routed through a powerful intermediary, which can lead to privilege escalation or confused deputy problems. Defenders reduce this risk with strict Kubernetes RBAC, least-privilege controller identities, admission controls, and careful review of custom resources, especially when manifests can affect cloud or organization-level resources.