Network Policies in Kubernetes Containers

Pods can "communicate" with endpoints and services without restrictions.

If a container/pod is invaded by an attacker, the attacker typically tries to access other containers/pods or the host machine. Network Policies prevent this attempt of the attacker.

We recommend creating a Network Policy with the Deny-All rule in each namespace and refraining from so-called Global Network Policies, as these are administratively confusing and pose a security risk.

  apiVersion: networking.k8s.io/v1
  kind: NetworkPolicy
  metadata:
    name: deny-all
    namespace: default ### should be created for all namespaces!
 spec:
    podSelector: {}
    policyTypes:
    - Ingress
    - Egress

After implementing the Deny-All rule, allow all permitted communications between the pods again with further Network Policies.

We also recommend that at least one person is in charge of the Network Policies.

Importance of the Deny-All Rule and Risks of Unrestricted Communication

While the Deny-All rule is mentioned, it's important to understand the implications of not implementing this rule:

Exposure to Sensitive Services: Without a Deny-All rule, all pods within the cluster can freely communicate with each other. This open communication can expose sensitive services or data stores to potentially compromised pods. An attacker who gains access to one pod can exploit this unrestricted communication to probe and access other services, leading to data breaches or unauthorized data manipulation.

Lateral Movement: In the absence of restrictive network policies, an attacker can move laterally within the cluster. Once inside a compromised pod, the attacker can easily attempt to access other pods and services, increasing the chances of compromising additional resources within the cluster.

Security Risk of Default Settings: Kubernetes clusters often have default settings that allow unrestricted pod-to-pod communication. This default configuration poses a significant security risk as it does not account for the potential of compromised pods attempting to exploit network connections.

Administrative Overhead and Confusion: Global Network Policies, while seemingly convenient, can lead to administrative confusion and increased security risks. They may inadvertently permit communication paths that should be restricted, leading to potential vulnerabilities. By creating namespace-specific Deny-All policies, you maintain clearer and more manageable security boundaries.

By implementing the Deny-All rule, you ensure that only explicitly allowed communications can occur within your cluster. This approach significantly reduces the attack surface and mitigates the risks associated with open communication policies, thus enhancing the overall security posture of your Kubernetes environment.