Do not admit containers wishing to share host network namespace

Error: Containers wishing to share host network namespace admitted

Bridgecrew Policy ID: BC_K8S_4
Checkov Check ID: CKV_K8S_4
Severity: MEDIUM

Containers wishing to share host network namespace admitted

Description

In a Kubernetes cluster, every pod gets its own IP address. Pods can be treated much like VMs or physical hosts from the perspectives of port allocation, naming, service discovery, load balancing, application configuration, and migration.

Sharing the host network namespace breaks the isolation between container images and can make the host visible to other containers in the pod. In some cases, pods in the host network of a node can communicate with all pods on all nodes without using network address translation (NAT).

Fix - Buildtime

Kubernetes

  • Resource: PodSecurityPolicy
  • Argument: hostNetwork (Optional)
    When set to false, Pods are unable to use their host's network namespace.
apiVersion: policy/v1beta1
kind: PodSecurityPolicy
metadata:
  name: <policy name>
spec:
+ hostNetwork: false

To use a PodSecurityPolicy resource, the requesting user or target pod’s service account must be authorized to use the policy. The preferred method is to grant access to the service account. In the following example we use RBAC, a standard Kubernetes authorization mode.

A Role or ClusterRole needs to grant access to use the desired policies.

Kind: ClusterRole

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: <role name>
rules:
- apiGroups: ['policy']
  resources: ['podsecuritypolicies']
  verbs:     ['use']
  resourceNames:
  - <policy name>

The ClusterRole is then bound to the authorized service(s):

Kind: ClusterRoleBinding

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: <binding name>
roleRef:
  kind: ClusterRole
  name: <role name>
  apiGroup: rbac.authorization.k8s.io
subjects:
- kind: ServiceAccount
  name: <authorized service account name>
  namespace: <authorized pod namespace>