Controller Manager bound to non loop-back insecure address

kube_controller_manager_bind_address

Severity

high

Vendor

Kubernetes

Resource

kube-controller-manager

Description

The Kubernetes controller manager is a daemon that embeds the core control loops shipped with Kubernetes.

The Controller Manager API service which runs on port 10252/TCP by default is used for health and metrics information and is available without authentication or encryption. As such it should only be bound to a localhost interface, to minimize the cluster’s attack surface.

Examples

apiVersion: v1
kind: Pod
metadata:
  name: bad
spec:
  containers:
  - command:
    - kube-controller-manager
    - --bind-address=0.0.0.0 (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	Command argument `--bind-address` not set to `127.0.0.1` means Controller Manager is bind to a non-loopback insecure address.

Mitigation / Fix

apiVersion: v1
kind: Pod
metadata:
  name: good
spec:
  containers:
  - command:
    - kube-controller-manager
    - --bind-address=127.0.0.1 (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	Command argument `--bind-address` set to `127.0.0.1` means Controller Manager is not bind to a non-loopback insecure address.