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Overview

Learn more about Kubernetes authorization, including details about creating policies using the supported authorization modules.

In Kubernetes, you must be authenticated (logged in) before your request can be authorized (granted permission to access). For information about authentication, see Accessing Control Overview.

Kubernetes expects attributes that are common to REST API requests. This means that Kubernetes authorization works with existing organization-wide or cloud-provider-wide access control systems which may handle other APIs besides the Kubernetes API.

Determine Whether a Request is Allowed or Denied

Kubernetes authorizes API requests using the API server. It evaluates all of the request attributes against all policies and allows or denies the request. All parts of an API request must be allowed by some policy in order to proceed. This means that permissions are denied by default.

(Although Kubernetes uses the API server, access controls and policies that depend on specific fields of specific kinds of objects are handled by Admission Controllers.)

When multiple authorization modules are configured, each is checked in sequence, and if any module authorizes the request, then the request can proceed. If all modules deny the request, then the request is denied (HTTP status code 403).

Review Your Request Attributes

Kubernetes reviews only the following API request attributes:

Determine the Request Verb

To determine the request verb for a resource API endpoint, review the HTTP verb used and whether or not the request acts on an individual resource or a collection of resources:

HTTP verb request verb
POST create
GET, HEAD get (for individual resources), list (for collections)
PUT update
PATCH patch
DELETE delete (for individual resources), deletecollection (for collections)

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

Authorization Modules

Checking API Access

Kubernetes exposes the subjectaccessreviews.v1.authorization.k8s.io resource as a normal resource that allows external access to API authorizer decisions. No matter which authorizer you choose to use, you can issue a POST with a SubjectAccessReview just like the webhook authorizer to the apis/authorization.k8s.io/v1/subjectaccessreviews endpoint and get back a response. For instance:

kubectl create --v=8 -f -  << __EOF__
{
  "apiVersion": "authorization.k8s.io/v1",
  "kind": "SubjectAccessReview",
  "spec": {
    "resourceAttributes": {
      "namespace": "kittensandponies",
      "verb": "get",
      "group": "unicorn.example.org",
      "resource": "pods"
    },
    "user": "jane",
    "group": [
      "group1",
      "group2"
    ],
    "extra": {
      "scopes": [
        "openid",
        "profile"
      ]
    }
  }
}
__EOF__

--- snip lots of output ---

I0913 08:12:31.362873   27425 request.go:908] Response Body: {"kind":"SubjectAccessReview","apiVersion":"authorization.k8s.io/v1","metadata":{"creationTimestamp":null},"spec":{"resourceAttributes":{"namespace":"kittensandponies","verb":"GET","group":"unicorn.example.org","resource":"pods"},"user":"jane","group":["group1","group2"],"extra":{"scopes":["openid","profile"]}},"status":{"allowed":true}}
subjectaccessreview "" created

This is useful for debugging access problems, in that you can use this resource to determine what access an authorizer is granting.

Using Flags for Your Authorization Module

You must include a flag in your policy to indicate which authorization module your policies include:

The following flags can be used:

You can choose more than one authorization module. If one of the modes is AlwaysAllow, then it overrides the other modes and all API requests are allowed.

Versioning

For version 1.2, clusters created by kube-up.sh are configured so that no authorization is required for any request.

As of version 1.3, clusters created by kube-up.sh are configured so that the ABAC authorization modules are enabled. However, its input file is initially set to allow all users to do all operations. The cluster administrator needs to edit that file, or configure a different authorizer to restrict what users can do.

What’s next

Privilege escalation via pod creation

Users who have ability to create pods in a namespace can potentially escalate their privileges within that namespace. They can create pods that access secrets the user cannot themselves read, or that run under a service account with different/greater permissions.

Caution: System administrators, use care when granting access to pod creation. A user granted permission to create pods (or controllers that create pods) in the namespace can: read all secrets in the namespace; read all config maps in the namespace; and impersonate any service account in the namespace and take any action the account could take. This applies regardless of authorization mode.

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