Cis K8s V200 4.2.4

---
name: cis-k8s-v200-4.2.4
description: "Verify that if defined, readOnlyPort is set to 0 (Manual)"
category: cis-k8s
version: "2.0.0"
author: cyberstrike-official
tags: [cis, kubernetes, worker-node, kubelet, read-only-port, network]
cis_id: "4.2.4"
cis_benchmark: "CIS Kubernetes Benchmark v2.0.0"
tech_stack: [kubernetes]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 4.2.4 Verify that if defined, readOnlyPort is set to 0 (Manual)

## Profile Applicability

- Level 1 - Worker Node

## Description

Disable the read-only port.

## Rationale

The Kubelet process provides a read-only API in addition to the main Kubelet API. Unauthenticated access is provided to this read-only API which could possibly retrieve potentially sensitive information about the cluster.

## Impact

Removal of the read-only port will require that any service which made use of it will need to be re-configured to use the main Kubelet API.

## Audit

Run the following command on each node:

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

Verify that the `--read-only-port` argument exists and is set to `0`.

If the `--read-only-port` argument is not present, check that there is a Kubelet config file specified by `--config`. Check that if there is a `readOnlyPort` entry in the file, it is set to `0`.

## Remediation

If using a Kubelet config file, edit the file to set `readOnlyPort` to `0`.

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_SYSTEM_PODS_ARGS` variable.

```bash
--read-only-port=0
```

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

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

## Default Value

By default, `--read-only-port` is set to `10255/TCP`. However, if a config file is specified by `--config` the default value for `readOnlyPort` is `0`.

## References

1. https://kubernetes.io/docs/admin/kubelet/
2. https://github.com/kubernetes/kubernetes/blob/6cedc0853faa118df0ba3d41b48b993422ad3df6/staging/src/k8s.io/kubelet/config/v1beta1/types.go#L142

## Additional Information

https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet/

## CIS Controls

| Controls Version | Control                                                                                                                                                                                                                                             | IG 1 | IG 2 | IG 3 |
| ---------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---- | ---- | ---- |
| v8               | 4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software - Uninstall or disable unnecessary services on enterprise assets and software, such as an unused file sharing service, web application module, or service function. |      | \*   | \*   |
| v7               | 9.2 Ensure Only Approved Ports, Protocols and Services Are Running - Ensure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.                                       |      | \*   | \*   |