Hands-on Lab·Certified Kubernetes Security Specialist
Restricting Kubernetes API Access
Restricting API access means three different things - who may call without a credential, what they get if they do, and who can reach the endpoint at all. This guide measures all three on a live cluster and closes the third with one policy.
Cluster Hardening Guide 12 of 40 Advanced
- Kubernetesapiserver v1.36.4, kubelet v1.36.3
- Runtimecontainerd 2.2.6
- CNICilium 1.18.1 - tunnel/VXLAN, with Hubble relay and UI
- Host OSUbuntu 26.04 LTS, kernel 7.0.0-29
- Built withkubeadm v1.36.3 - podSubnet 10.244.0.0/16, serviceSubnet 10.96.0.0/12
- TimeAbout 18 min
- Reviewed25 August 2026
Written against the versions above. `--anonymous-auth` is not set on this apiserver, so it defaults to true. Authorization mode is `Node,RBAC`, which is what turns an anonymous request into a 403 rather than a 200.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| CKA6001 | 192.168.0.46 | Ubuntu 26.04 LTS | Control Plane Node (tainted NoSchedule) | 2 Core | 4 GB | 50 GB |
| CKA6001-NODE01 | 192.168.0.47 | Ubuntu 26.04 LTS | Worker Node | 2 Core | 4 GB | 50 GB |
| CKA6001-NODE02 | 192.168.0.48 | Ubuntu 26.04 LTS | Worker Node | 2 Core | 4 GB | 50 GB |
Before you start
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What the apiserver answers with no credential at all
-
The flags and the bindings that decide it
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Every Pod can reach the control plane