cis-ocp-v190-3.1.1

DevOps & Security

Client certificate authentication should not be used for users (Manual)

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CIS Red Hat OpenShift Container Platform Benchmark v1.9.0 - Control 3.1.1

Profile Applicability

Level: 2

Description

Kubernetes provides the option to use client certificates for user authentication. However as there is no way to revoke these certificates when a user leaves an organization or loses their credential, they are not suitable for this purpose.

It is not possible to fully disable client certificate use within a cluster as it is used for component to component authentication.

Rationale

With any authentication mechanism the ability to revoke credentials if they are compromised or no longer required, is a key control. Kubernetes client certificate authentication does not allow for this due to a lack of support for certificate revocation.

Impact

External mechanisms for authentication generally require additional software to be deployed.

Audit Procedure

For users to interact with OpenShift Container Platform, they must first authenticate to the cluster. The authentication layer identifies the user with requests to the OpenShift Container Platform API. The authorization layer then uses information about the requesting user to determine if the request is allowed.

The OpenShift Container Platform includes a built-in OAuth server for token-based authentication. Developers and administrators obtain OAuth access tokens to authenticate themselves to the API. It is recommended for an administrator to configure OAuth to specify an identity provider after the cluster is installed. User access to the cluster is managed through the identity provider.

First, verify user authentication is enabled:

oc describe authentication

Next, verify an identity provider is configured:

oc get oauth -o json | jq '.items[].spec.identityProviders'

Verify at least one identity provider is configured, and verify that the kubeadmin user does not exist.

Next, verify a cluster-admin user exists:

oc get clusterrolebindings -o='custom-columns=NAME:.metadata.name,ROLE:.roleRef.name,SUBJECT:.subjects[*].kind' | grep cluster-admin | grep User

Verify at least one user has the cluster-admin role.

Finally, verify that the kubeadmin secret is removed:

oc get secrets kubeadmin -n kube-system

No result is expected.

Remediation

Configure an identity provider for the OpenShift cluster following the OpenShift documentation. Once an identity provider has been defined, you can use RBAC to define and apply permissions.

After you define an identity provider and create a new cluster-admin user you can reduce the attack surface by removing the default kubeadmin user.

Default Value

By default, only a kubeadmin user exists on your cluster. To specify an identity provider, you must create a Custom Resource (CR) that describes that identity provider and add it to the cluster.

References

CIS Controls

Controls Version	Control	IG 2	IG 3
v8	4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software	X	X
v8	16.11 Leverage Vetted Modules or Services for Application Security Components	X	X
v7	16.2 Configure Centralized Point of Authentication	X	X

MITRE ATT&CK Mappings

Techniques / Sub-techniques	Tactics	Mitigations
T1078, T1098	TA0003, TA0006	M1027, M1032

Profile

Level 2 (Manual)