Cis K8S V1110 1.2.29

1.2.29 Ensure that the API Server only makes use of Strong Cryptographic Ciphers (Manual)

Profile Applicability

• Level 1 - Master Node

Description

Ensure that the API server is configured to only use strong cryptographic ciphers.

Rationale

TLS ciphers have had a number of known vulnerabilities and weaknesses, which can reduce the protection provided by them. By default Kubernetes supports a number of TLS cipher suites including some that have security concerns, weakening the protection provided.

Impact

API server clients that cannot support modern cryptographic ciphers will not be able to make connections to the API server.

Audit

Run the following command on the Control Plane node:

ps -ef | grep kube-apiserver

Verify that the --tls-cipher-suites argument is set as outlined in the remediation procedure below.

Remediation

Edit the API server pod specification file /etc/kubernetes/manifests/kube-apiserver.yaml on the Control Plane node and set the below parameter.

--tls-cipher-suites=TLS_AES_128_GCM_SHA256, TLS_AES_256_GCM_SHA384,
TLS_CHACHA20_POLY1305_SHA256, TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256.

Default Value

By default the Kubernetes API server supports a wide range of TLS ciphers.

Additional Information

Insecure values: TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256, TLS_ECDHE_ECDSA_WITH_RC4_128_SHA, TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256, TLS_ECDHE_RSA_WITH_RC4_128_SHA, TLS_RSA_WITH_3DES_EDE_CBC_SHA, TLS_RSA_WITH_AES_128_CBC_SHA, TLS_RSA_WITH_AES_128_CBC_SHA256, TLS_RSA_WITH_AES_128_GCM_SHA256, TLS_RSA_WITH_AES_256_CBC_SHA, TLS_RSA_WITH_AES_256_GCM_SHA384, TLS_RSA_WITH_RC4_128_SHA.

References

1. https://kubernetes.io/docs/reference/command-line-tools-reference/kube-apiserver/
2. https://github.com/ssllabs/research/wiki/SSL-and-TLS-Deployment-Best-Practices#23-use-secure-cipher-suites

CIS Controls