OWASP Cheat Sheet Series: Kubernetes Security Cheat Sheet

# Kubernetes Security Cheat Sheet

## Overview

This cheat sheet provides a starting point for securing a Kubernetes cluster. It is divided into the following categories:

- Receive Alerts for Kubernetes Updates
- INTRODUCTION: What is Kubernetes?
- Securing Kubernetes hosts
- Securing Kubernetes components
- Using the Kubernetes dashboard
- Kubernetes Security Best Practices: Build Phase
- Kubernetes Security Best Practices: Deploy Phase
- Kubernetes Security Best Practices: Runtime Phase

For more information about Kubernetes, refer to the Appendix.

## Receive Alerts for Security Updates and Reporting Vulnerabilities

Join the kubernetes-announce group (<https://kubernetes.io/docs/reference/issues-security/security/>) for emails about security announcements. See the security reporting page (<https://kubernetes.io/docs/reference/issues-security/security>) for more on how to report vulnerabilities.

## INTRODUCTION: What Is Kubernetes?

Kubernetes is an open source container orchestration engine for automating deployment, scaling, and management of containerized applications. The open source project is hosted by the Cloud Native Computing Foundation (CNCF).

When you deploy Kubernetes, you get a cluster. A Kubernetes cluster consists of a set of worker machines, called nodes that run containerized applications. The control plane manages the worker nodes and the Pods in the cluster.

### Control Plane Components

The control plane's components make global decisions about the cluster, as well as detecting and responding to cluster events. It consists of components such as kube-apiserver, etcd, kube-scheduler, kube-controller-manager and cloud-controller-manager.

**Component:** kube-apiserver  
**Description:** Exposes the Kubernetes API. The API server is the front end for the Kubernetes control plane.

**Component:** etcd  
**Description:** A consistent and highly-available key-value store used as Kubernetes' backing store for all cluster data.

**Component:** kube-scheduler  
**Description:** Watches for newly created Pods with no assigned node, and selects a node for them to run on.

**Component:** kube-controller-manager  
**Description:** Runs controller processes. Logically, each controller is a separate process, but to reduce complexity, they are all compiled into a single binary and run in a single process.

**Component:** cloud-controller-manager  
**Description:** The cloud controller manager lets you link your cluster into your cloud provider's API, and separates out the components that interact with that cloud platform from components that just interact with your cluster.

### Node Components

Node components run on every node, maintaining running pods and providing the Kubernetes runtime environment. It consists of components such as kubelet, kube-proxy and container runtime.

**Component:** kubelet  
**Description:** An agent that runs on each node in the cluster. It makes sure that containers are running in a Pod.

**Component:** kube-proxy  
**Description:** A network proxy that runs on each node in your cluster, implementing part of the Kubernetes Service concept.

**Container:** runtime  
**Description:** The container runtime is the software that is responsible for running containers |

## SECTION 1: Securing Kubernetes Hosts

Kubernetes can be deployed in different ways: on bare metal, on-premise, and in the public cloud (a custom Kubernetes build on virtual machines OR use a managed service). Since Kubernetes is designed to be highly portable, customers can easily and migrate their workloads and switch between multiple installations.

Because Kubernetes can be designed to fit a large variety of scenarios, this flexibility is a weakness when it comes to securing Kubernetes clusters. The engineers responsible for deploying the Kubernetes platform must know about all the potential attack vectors and vulnerabilities for their clusters.

To harden the underlying hosts for Kubernetes clusters, we recommend that you install the latest version of the operating systems, harden the operating systems, implement necessary patch management and configuration management systems, implement essential firewall rules and undertake specific datacenter-based security measures.

### Updating Kubernetes

Since no one can track all potential attack vectors for your Kubernetes cluster, the first and best defense is to always run the latest stable version of Kubernetes.

In case vulnerabilities are found in running containers, it is recommended to always update the source image and redeploy the containers. **Try to avoid direct updates to the running containers as this can break the image-container relationship.**

```
Example: apt-update
```

**Upgrading containers is extremely easy with the Kubernetes rolling updates feature - this allows gradually updating a running application by upgrading its images to the latest version.**

#### Release schedule for Kubernetes

The Kubernetes project maintains release branches for the most recent three minor releases and it backports the applicable fixes, including security fixes, to those three release branches, depending on severity and feasibility. Patch releases are cut from those branches at a regular cadence, plus additional urgent releases, when required. Hence it is always recommended to upgrade the Kubernetes cluster to the latest available stable version. It is recommended to refer to the version skew policy for further details <https://kubernetes.io/docs/setup/release/version-skew-policy/>.

There are several techniques such as rolling updates, and node pool migrations that allow you to complete an update with minimal disruption and downtime.

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## SECTION 2: Securing Kubernetes Components

This section discusses how to secure Kubernetes components. It covers the following topics:

- Securing the Kubernetes Dashboard
- Restricting access to etcd (Important)
- Controlling network access to sensitive ports
- Controlling access to the Kubernetes API
- Implementing role-based access control in Kubernetes
- Limiting access to Kubelets

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### Securing the Kubernetes Dashboard

The Kubernetes dashboard is a webapp for managing your cluster. It is not a part of the Kubernetes cluster itself, it has to be installed by the owners of the cluster. Thus, there are a lot of tutorials on how to do this. Unfortunately, most of them create a service account with very high privileges. This caused Tesla and some others to be hacked via such a poorly configured K8s dashboard. (Reference: Tesla cloud resources are hacked to run cryptocurrency-mining malware - <https://arstechnica.com/information-technology/2018/02/tesla-cloud-resources-are-hacked-to-run-cryptocurrency-mining-malware/>)

To prevent attacks via the dashboard, you should follow some tips:

- Do not expose the dashboard without additional authentication to the public. There is no need to access such a powerful tool from outside your LAN
- Turn on Role-Based Access Control (see