Cis Oke V150 3.2.3

---
name: cis-oke-v150-3.2.3
description: "Ensure that the --client-ca-file argument is set as appropriate (Automated)"
category: cis-oke
version: "1.5.0"
author: cyberstrike-official
tags: [cis, oke, kubernetes, oci, worker-node, kubelet]
cis_id: "3.2.3"
cis_benchmark: "CIS Oracle Cloud Infrastructure Container Engine for Kubernetes (OKE) Benchmark v1.5.0"
tech_stack: [kubernetes, oci, oke]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

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

## Profile Applicability

- Level 1

## 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 Procedure

**Audit Method 1:**
If using a Kubelet configuration file, check that there is an entry for `--client-ca-file` set to the location of the client certificate authority file.
First, SSH to the relevant node:
Run the following command on each node to find the appropriate Kubelet config file:

```bash
find / -name kubelet.service
```

The output of the above command should return the file and location `/etc/systemd/system/kublet.service` which is the location of the Kubelet service config file.
Open the Kubelet service config file:

```bash
sudo more etc/systemd/system/kublet.service
```

Verify that the `--client-ca-file` argument exists and is set to the location of the client certificate authority file.

**Audit Method 2:**
If using the api configz endpoint consider searching for the status of `authentication..x509":{"clientCAFile":"/etc/kubernetes/ca.crt` by extracting the live configuration from the nodes running kubelet.
Set the local proxy port and the following variables and provide proxy port number and node name;
`HOSTNAME_PORT="localhost-and-port-number"`
`NODE_NAME="The-Name-Of-Node-To-Extract-Configuration"` from the output of `"kubectl get nodes"`

```bash
kubectl proxy --port=8001 &

export HOSTNAME_PORT=localhost:8001 (example host and port number)
export NODE_NAME=10.0.10.4 (example node name from "kubectl get nodes")

curl -sSL "http://${HOSTNAME_PORT}/api/v1/nodes/${NODE_NAME}/proxy/configz"
```

## Remediation

**Remediation Method 1:**
If modifying the Kubelet service config file, edit the kubelet.service file `/etc/systemd/system/kubelet.service` and set the below parameter

```
--client-ca-file=/etc/kubernetes/ca.crt \
```

**Remediation Method 2:**
If using the api configz endpoint consider searching for the status of `"authentication.*x509":{"clientCAFile":"/etc/kubernetes/pki/ca.crt"` by extracting the live configuration from the nodes running kubelet.
\*\*See detailed step-by-step configmap procedures in Reconfigure a Node's Kubelet in a Live Cluster, and then rerun the curl statement from audit process to check for kubelet configuration changes

```bash
kubectl proxy --port=8001 &

export HOSTNAME_PORT=localhost:8001 (example host and port number)
export NODE_NAME=10.0.10.4 (example node name from "kubectl get nodes")

curl -sSL "http://${HOSTNAME_PORT}/api/v1/nodes/${NODE_NAME}/proxy/configz"
```

For all remediations:
Based on your system, restart the `kubelet` service and check status

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

## Default Value

See the OKE documentation for the default value.

## 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/)
3. [https://docs.cloud.oracle.com/en-us/iaas/Content/ContEng/Concepts/contengoverview.htm](https://docs.cloud.oracle.com/en-us/iaas/Content/ContEng/Concepts/contengoverview.htm)

## 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    |

## MITRE ATT&CK Mappings

| Techniques / Sub-techniques | Tactics | Mitigations |
| --------------------------- | ------- | ----------- |
| T1552                       | TA0006  | M1022       |

---

**Profile:** Level 1 - CIS Oracle Cloud Infrastructure Container Engine for Kubernetes (OKE) Benchmark v1.5.0