cis-k8s-v1111-3.1.1

DevOps & Security

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

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

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

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.

References

None

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	6.2 Establish an Access Revoking Process	x	x	x
v7	16.7 Establish Process for Revoking Access		x	x