Cis K8s V1110 1.2.5

---
name: cis-k8s-v1110-1.2.5
description: "Ensure that the --kubelet-certificate-authority argument is set as appropriate (Automated)"
category: cis-k8s
version: "1.11.0"
author: cyberstrike-official
tags: [cis, kubernetes, control-plane, api-server, kubelet-certificate-authority, tls, certificate-validation]
cis_id: "1.2.5"
cis_benchmark: "CIS Kubernetes Benchmark v1.11.0"
tech_stack: [kubernetes]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 1.2.5 Ensure that the --kubelet-certificate-authority argument is set as appropriate (Automated)

## Profile Applicability

- Level 1 - Master Node

## Description

Verify kubelet's certificate before establishing connection.

## Rationale

The connections from the apiserver to the kubelet are used for fetching logs for pods, attaching (through kubectl) to running pods, and using the kubelet's port-forwarding functionality. These connections terminate at the kubelet's HTTPS endpoint. By default, the apiserver does not verify the kubelet's serving certificate, which makes the connection subject to man-in-the-middle attacks, and unsafe to run over untrusted and/or public networks.

## Impact

You require TLS to be configured on apiserver as well as kubelets.

## Audit

Run the following command on the Control Plane node:

```bash
ps -ef | grep kube-apiserver
```

Verify that the `--kubelet-certificate-authority` argument exists and is set as appropriate.

Alternative Audit:

```bash
kubectl get pod -nkube-system -lcomponent=kube-apiserver -o=jsonpath='{range .items[]}{.spec.containers[].command} {"\n"}{end}' | grep '--kubelet-certificate-Authority' | grep -i false
```

If the exit code is '1', then the control isn't present / failed.

## Remediation

Follow the Kubernetes documentation and setup the TLS connection between the apiserver and kubelets. Then, edit the API server pod specification file `/etc/kubernetes/manifests/kube-apiserver.yaml` on the Control Plane node and set the `--kubelet-certificate-authority` parameter to the path to the cert file for the certificate authority.

```
--kubelet-certificate-authority=<ca-string>
```

## Default Value

By default, `--kubelet-certificate-authority` argument is not set.

## References

1. https://kubernetes.io/docs/admin/kube-apiserver/
2. https://kubernetes.io/docs/admin/kubelet-authentication-authorization/
3. https://kubernetes.io/docs/concepts/cluster-administration/master-node-communication/#apiserver---kubelet

## CIS Controls

| Controls Version | Control                                                                       | IG 1 | IG 2 | IG 3 |
| ---------------- | ----------------------------------------------------------------------------- | ---- | ---- | ---- |
| v8               | 16.11 Leverage Vetted Modules or Services for Application Security Components |      | \*   | \*   |
| v7               | 9 Limitation and Control of Network Ports, Protocols, and Services            |      |      |      |