# Kubernetes Role-Based Access Control (RBAC)

## Role-Based Access Control (RBAC)

Kubernetes has an **authorization module named Role-Based Access Control** ([**RBAC**](https://kubernetes.io/docs/reference/access-authn-authz/rbac/)) that helps to set utilization permissions to the API server.\
The RBAC table is constructed from “**Roles**” and “**ClusterRoles**.” The difference between them is just where the role will be applied – a “**Role**” will grant access to only **one** **specific** **namespace**, while a “**ClusterRole**” can be used in **all namespaces** in the cluster. Moreover, ClusterRoles can also grant access to:

* cluster-scoped resources (like nodes).
* non-resource endpoints (like /healthz).
* namespaced resources (like Pods), across all namespaces.

In the template of a role or a cluster role you will need to indicate the **name of the role**, the **namespace** (in roles) and then the **apiGroups**, **resources** and **verbs** of the role:

* The **apiGroups** is an array that contains the different **API namespaces** that this rule applies to. For example, a Pod definition uses apiVersion: v1. _It can has values such as rbac.authorization.k8s.io or \[\*]_.
* The **resources** is an array that defines **which resources this rule applies to**. You can find all the resources with: `kubectl api-resources --namespaced=true`
* The **verbs** is an array that contains the **allowed verbs**. The verb in Kubernetes defines the **type of action** you need to apply to the resource. For example, the list verb is used against collections while "get" is used against a single resource.

### Rules Verbs

(_This info was taken from_ [_**here**_](https://kubernetes.io/docs/reference/access-authn-authz/authorization/#determine-the-request-verb))

| HTTP verb | request verb                                                                                                                                                  |
| --------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| POST      | create                                                                                                                                                        |
| GET, HEAD | get (for individual resources), list (for collections, including full object content), watch (for watching an individual resource or collection of resources) |
| PUT       | update                                                                                                                                                        |
| PATCH     | patch                                                                                                                                                         |
| DELETE    | delete (for individual resources), deletecollection (for collections)                                                                                         |

Kubernetes sometimes checks authorization for additional permissions using specialized verbs. For example:

* [PodSecurityPolicy](https://kubernetes.io/docs/concepts/policy/pod-security-policy/)
  * `use` verb on `podsecuritypolicies` resources in the `policy` API group.
* [RBAC](https://kubernetes.io/docs/reference/access-authn-authz/rbac/#privilege-escalation-prevention-and-bootstrapping)
  * `bind` and `escalate` verbs on `roles` and `clusterroles` resources in the `rbac.authorization.k8s.io` API group.
* [Authentication](https://kubernetes.io/docs/reference/access-authn-authz/authentication/)
  * `impersonate` verb on `users`, `groups`, and `serviceaccounts` in the core API group, and the `userextras` in the `authentication.k8s.io` API group.

{% hint style="warning" %}
You can find **all the verbs that each resource support** executing `kubectl api-resources --sort-by name -o wide`
{% endhint %}

### Examples

Example of **Role** **configuration**:

```yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: defaultGreen
  name: pod-and-pod-logs-reader
rules:
- apiGroups: [""]
  resources: ["pods", "pods/log"]
  verbs: ["get", "list", "watch"]
```

Example of **ClusterRole** configuration:

```yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  # "namespace" omitted since ClusterRoles are not namespaced
  name: secret-reader
rules:
- apiGroups: [""]
  resources: ["secrets"]
  verbs: ["get", "watch", "list"]
```

For example you can use a **ClusterRole** to allow a particular user to run:

```
kubectl get pods --all-namespaces
```

**Role and ClusterRole Binding concept**

A **role binding** **grants the permissions defined in a role to a user or set of users**. It holds a list of subjects (users, groups, or service accounts), and a reference to the role being granted. A **RoleBinding** grants permissions within a specific **namespace** whereas a **ClusterRoleBinding** grants that access **cluster-wide**.

**RoleBinding** example:

```yaml
apiVersion: rbac.authorization.k8s.io/v1
# This role binding allows "jane" to read pods in the "default" namespace.
# You need to already have a Role named "pod-reader" in that namespace.
kind: RoleBinding
metadata:
  name: read-pods
  namespace: default
subjects:
# You can specify more than one "subject"
- kind: User
  name: jane # "name" is case sensitive
  apiGroup: rbac.authorization.k8s.io
roleRef:
  # "roleRef" specifies the binding to a Role / ClusterRole
  kind: Role #this must be Role or ClusterRole
  name: pod-reader # this must match the name of the Role or ClusterRole you wish to bind to
  apiGroup: rbac.authorization.k8s.io
```

**ClusterRoleBinding** example:

```yaml
apiVersion: rbac.authorization.k8s.io/v1
# This cluster role binding allows anyone in the "manager" group to read secrets in any namespace.
kind: ClusterRoleBinding
metadata:
  name: read-secrets-global
subjects:
- kind: Group
  name: manager # Name is case sensitive
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: ClusterRole
  name: secret-reader
  apiGroup: rbac.authorization.k8s.io
```

**Permissions are additive** so if you have a clusterRole with “list” and “delete” secrets you can add it with a Role with “get”. So be aware and test always your roles and permissions and **specify what is ALLOWED, because everything is DENIED by default.**

### **Enumerating RBAC**

```bash
# Get current privileges
kubectl auth can-i --list
## use `--as=system:serviceaccount:<namespace>:<sa_name>` to impersonate a service account

# List Cluster Roles
kubectl get clusterroles
kubectl describe clusterroles

# List Cluster Roles Bindings
kubectl get clusterrolebindings
kubectl describe clusterrolebindings

# List Roles
kubectl get roles
kubectl describe roles

# List Roles Bindings
kubectl get rolebindings
kubectl describe rolebindings
```

### RBAC Structure

RBAC’s permission is built from three individual parts:

1. **Role\ClusterRole ­–** The actual permission. It contains _**rules**_ that represent a set of permissions. Each rule contains [resources](https://kubernetes.io/docs/reference/kubectl/overview/#resource-types) and [verbs](https://kubernetes.io/docs/reference/access-authn-authz/authorization/#determine-the-request-verb). The verb is the action that will apply on the resource.
2. **Subject (User, Group or ServiceAccount) –** The object that will receive the permissions.
3. **RoleBinding\ClusterRoleBinding –** The connection between Role\ClusterRole and the subject.

This is what it will look like in a real cluster:

![](https://www.cyberark.com/wp-content/uploads/2018/12/rolebiding\_serviceaccount\_and\_role-1024x551.png)

“**Fine-grained** role bindings **provide greater security**, but **require more effort to administrate**."

From **Kubernetes** 1.6 onwards, **RBAC** policies are **enabled by default**. **** But to enable RBAC you can use something like:

```
kube-apiserver --authorization-mode=Example,RBAC --other-options --more-options
```

This is enabled by default. RBAC functions:

* Restrict the access to the resources to users or ServiceAccounts.
* An RBAC Role or ClusterRole contains rules that represent a set of permissions.
* Permissions are purely additive (there are no “deny” rules).
* RBAC works with Roles and Bindings

{% hint style="info" %}
When configuring roles and permissions it's highly important to always follow the principle of Least Privileges
{% endhint %}