cis-k8s-v200-3.1.1

DevOps & Security

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

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CIS Kubernetes Benchmark v2.0.0 - Control 3.1.1

Profile Applicability

Level: 1 - Master Node

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

Review user access to the cluster and ensure that users are not making use of Kubernetes client certificate authentication.

Remediation

Alternative mechanisms provided by Kubernetes such as the use of OIDC should be implemented in place of client certificates.

Default Value

Client certificate authentication is enabled by default.

Additional Information

The lack of certificate revocation was flagged up as a high risk issue in the recent Kubernetes security audit. Without this feature, client certificate authentication is not suitable for end users.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	6.2 Establish an Access Revoking ProcessEstablish and follow a process, preferably automated, for revoking access to enterprise assets, through disabling accounts immediately upon termination, rights revocation, or role change of a user. Disabling accounts, instead of deleting accounts, may be necessary to preserve audit trails.	●	●	●
v7	16.7 Establish Process for Revoking AccessEstablish and follow an automated process for revoking system access by disabling accounts immediately upon termination or change of responsibilities of an employee or contractor. Disabling these accounts, instead of deleting accounts, allows preservation of audit trails.		●	●

Profile

Level 1 - Master Node (Manual)