# Cis K8S V1110 4.2.3

> Ensure that the --client-ca-file argument is set as appropriate (Automated)

- Skill: `cyberstrikeus/cis-k8s-v1110-4-2-3` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-k8s-v1110-4-2-3`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-k8s-v1110-4-2-3/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-k8s-v1110-4-2-3

---


# 4.2.3 Ensure that the --client-ca-file argument is set as appropriate (Automated)

## Profile Applicability

- Level 1 - Worker Node

## Description

Enable Kubelet authentication using certificates.

## 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. Enabling Kubelet certificate authentication ensures that the apiserver could authenticate the Kubelet before submitting any requests.

## Impact

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

## Audit

Run the following command on each node:

```bash
ps -ef | grep kubelet
```

Verify that the `--client-ca-file` argument exists and is set to the location of the client certificate authority file.
If the `--client-ca-file` argument is not present, check that there is a Kubelet config file specified by `--config`, and that the file sets `authentication: x509: clientCAFile` to the location of the client certificate authority file.

## Remediation

If using a Kubelet config file, edit the file to set `authentication: x509: clientCAFile` to the location of the client CA file.
If using command line arguments, edit the kubelet service file `/etc/kubernetes/kubelet.conf` on each worker node and set the below parameter in `KUBELET_AUTHZ_ARGS` variable.

```
--client-ca-file=<path/to/client-ca-file>
```

Based on your system, restart the `kubelet` service. For example:

```bash
systemctl daemon-reload
systemctl restart kubelet.service
```

## Default Value

By default, `--client-ca-file` argument is not set.

## References

1. [https://kubernetes.io/docs/admin/kubelet/](https://kubernetes.io/docs/admin/kubelet/)
2. [https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-authentication-authorization/](https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-authentication-authorization/)

## CIS Controls

| Controls Version | Control                                           | IG 1 | IG 2 | IG 3 |
| ---------------- | ------------------------------------------------- | ---- | ---- | ---- |
| v8               | 3.10 Encrypt Sensitive Data in Transit            |      | x    | x    |
| v7               | 14.4 Encrypt All Sensitive Information in Transit |      | x    | x    |