CIS-1.2.31 - Ensure that the API Server only makes use of Strong Cryptographic Ciphers

Ensure that the API Server only makes use of Strong Cryptographic Ciphers

Framework

CIS

Severity

Medium

Description of the the issue

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 ciphersuites including some that have security concerns, weakening the protection provided.

Related resources

Pod

What does this control test

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

How to check it manually

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_3DES_EDE_CBC_SHA, 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, TLS_RSA_WITH_3DES_EDE_CBC_SHA, TLS_RSA_WITH_AES_128_CBC_SHA, TLS_RSA_WITH_AES_128_GCM_SHA256, TLS_RSA_WITH_AES_256_CBC_SHA, TLS_RSA_WITH_AES_256_GCM_SHA384.

Impact Statement

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

Default Value

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

Example

No example