Apiserver allows weak cryptographic ciphers

api_server_strong_cryptographic_ciphers

Severity

critical

Vendor

Kubernetes

Resource

kube-apiserver

Description

By default, Kubernetes supports weak cryptographic ciphers which can have security vulnerability issues.

Thus, setting --tls-cipher-suites with a proper cipher suite value is mandatory to keep TLS protection safe.

Examples

apiVersion: v1
kind: Pod
metadata:
  name: bad
spec:
  containers:
  - command:
    - kube-apiserver
    - --tls-cipher-suites=TLS_RSA_WITH_RC4_128_SHA (1)
    image: gcr.io/google_containers/kube-apiserver-amd64:v1.9.0
    name: bad-container
    livenessProbe:
      failureThreshold: 8
      httpGet:
        host: 127.0.0.1
        path: /health
        port: 6443
        scheme: HTTPS
      initialDelaySeconds: 15
      timeoutSeconds: 15
    resources:
      requests:
        cpu: 250m
    volumeMounts:
    - mountPath: /etc/kubernetes/
      name: k8s
      readOnly: true
    - mountPath: /etc/ssl/certs
      name: certs
    - mountPath: /etc/pki
      name: pki
  hostNetwork: true
  volumes:
  - hostPath:
      path: /etc/kubernetes
    name: k8s
  - hostPath:
      path: /etc/ssl/certs
    name: certs
  - hostPath:
      path: /etc/pki
    name: pki

1	Using a weak cryptographic cipher in the `--tls-cipher-suites` command argument means TLS protection is broken.

Mitigation / Fix

apiVersion: v1
kind: Pod
metadata:
  name: good
spec:
  containers:
  - command:
    - kube-apiserver
    - --tls-cipher-suites=TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (1)
    image: gcr.io/google_containers/kube-apiserver-amd64:v1.9.0
    name: good-container
    livenessProbe:
      failureThreshold: 8
      httpGet:
        host: 127.0.0.1
        path: /health
        port: 6443
        scheme: HTTPS
      initialDelaySeconds: 15
      timeoutSeconds: 15
    resources:
      requests:
        cpu: 250m
    volumeMounts:
    - mountPath: /etc/kubernetes/
      name: k8s
      readOnly: true
    - mountPath: /etc/ssl/certs
      name: certs
    - mountPath: /etc/pki
      name: pki
  hostNetwork: true
  volumes:
  - hostPath:
      path: /etc/kubernetes
    name: k8s
  - hostPath:
      path: /etc/ssl/certs
    name: certs
  - hostPath:
      path: /etc/pki
    name: pki

1	Only strong cryptographic cipher suites are allowed.

Configuration

The list of allowed TLS cipher suites can be configured in the allowedCiphers property.

Recommended cipher suites are:

TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
TLS_RSA_WITH_AES_256_GCM_SHA384
TLS_RSA_WITH_AES_128_GCM_SHA256