171 lines
7.9 KiB
Markdown
171 lines
7.9 KiB
Markdown
# 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.
|
||
|
||
RBAC’s permission model 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.
|
||
|
||
|
||
|
||
The difference between “**Roles**” and “**ClusterRoles**” 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**.
|
||
|
||
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
|
||
```
|
||
|
||
## Templates
|
||
|
||
In the template of a **Role** or a **ClusterRole** 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
|
||
|
||
{% code title="Role" %}
|
||
```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"]
|
||
```
|
||
{% endcode %}
|
||
|
||
{% code title="ClusterRole" %}
|
||
```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"]
|
||
```
|
||
{% endcode %}
|
||
|
||
For example you can use a **ClusterRole** to allow a particular user to run:
|
||
|
||
```
|
||
kubectl get pods --all-namespaces
|
||
```
|
||
|
||
### **RoleBinding and ClusterRoleBinding**
|
||
|
||
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**.
|
||
|
||
{% code title="" %}
|
||
```yaml
|
||
piVersion: 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
|
||
```
|
||
{% endcode %}
|
||
|
||
{% code title="ClusterRoleBinding" %}
|
||
```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
|
||
```
|
||
{% endcode %}
|
||
|
||
**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
|
||
```
|
||
|
||
### Abuse Role/ClusterRoles for Privilege Escalation
|
||
|
||
{% content-ref url="hardening-roles-clusterroles/" %}
|
||
[hardening-roles-clusterroles](hardening-roles-clusterroles/)
|
||
{% endcontent-ref %}
|