Ensure That All Namespaces Have Network Policies Defined

More Info:

Without NetworkPolicies, pods accept traffic from any source by default. Every namespace should define at least one NetworkPolicy to control pod-level traffic.

Risk Level

High

Address

Security

Compliance Standards

• CIS AKS

Triage and Remediation

Remediation

Remediation

Manual Steps

1. Identify namespaces missing NetworkPolicies (run on any machine with kubectl access):

   ns_without_np=$(comm -23 \
     <(kubectl get ns -o jsonpath='{.items[*].metadata.name}' | tr ' ' '\n' | sort) \
     <(kubectl get networkpolicy --all-namespaces -o jsonpath='{.items[*].metadata.namespace}' | tr ' ' '\n' | sort))
   
   printf '%s\n' "$ns_without_np"

2. For each namespace that needs a strict default, create a default-deny-all policy (run on any machine with kubectl access; replace NAMESPACE with one from the list above):

   kubectl apply -n NAMESPACE -f - <<'EOF'
   apiVersion: networking.k8s.io/v1
   kind: NetworkPolicy
   metadata:
     name: default-deny-all
   spec:
     podSelector: {}
     policyTypes:
       - Ingress
       - Egress
   EOF

3. For namespaces where you cannot fully deny all traffic, create an initial restrictive policy and adjust later (example allowing only intra-namespace traffic; run on any machine with kubectl access and replace NAMESPACE):

   kubectl apply -n NAMESPACE -f - <<'EOF'
   apiVersion: networking.k8s.io/v1
   kind: NetworkPolicy
   metadata:
     name: restrict-to-namespace
   spec:
     podSelector: {}
     policyTypes:
       - Ingress
   ingress:
     - from:
       - podSelector: {}
   EOF

4. Review and customize policies in critical namespaces (e.g., kube-system, monitoring, ingress) to avoid breaking traffic (run on any machine with kubectl access):

   # List policies in a namespace
   kubectl get networkpolicy -n NAMESPACE
   
   # Show details of a policy
   kubectl describe networkpolicy -n NAMESPACE POLICY_NAME
   
   # Edit a policy in-place
   kubectl edit networkpolicy -n NAMESPACE POLICY_NAME

5. Optionally export policies to manifests for version control (run on any machine with kubectl access):

   kubectl get networkpolicy -A -o yaml > all-networkpolicies-backup.yaml

6. Verification (run on any machine with kubectl access):

   ns_without_np=$(comm -23 \
     <(kubectl get ns -o jsonpath='{.items[*].metadata.name}' | tr ' ' '\n' | sort) \
     <(kubectl get networkpolicy --all-namespaces -o jsonpath='{.items[*].metadata.namespace}' | tr ' ' '\n' | sort))
   
   if [ -z "$ns_without_np" ]; then
     echo "ALL_NAMESPACES_HAVE_NETWORKPOLICIES"
   else
     echo "MISSING_NETWORKPOLICIES"
     printf '%s\n' "$ns_without_np"
   fi

Using kubectl

On any machine with kubectl access to the cluster:

1. List namespaces currently missing NetworkPolicies (for your awareness):

ns_without_np=$(comm -23 \
  <(kubectl get ns -o jsonpath='{.items[*].metadata.name}' | tr ' ' '\n' | sort) \
  <(kubectl get networkpolicy --all-namespaces -o jsonpath='{.items[*].metadata.namespace}' | tr ' ' '\n' | sort))

printf '%s\n' "$ns_without_np"

2. Create a default-deny NetworkPolicy in each namespace that lacks one (replace the namespace list as needed, or paste from the previous command’s output):

for ns in kube-system default; do
  kubectl apply -n "$ns" -f - <<EOF
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress
EOF
done

Adjust the for ns in ... list to include every namespace that should receive a default-deny policy, based on your environment and application needs.

3. Verification (same command used by the audit):

ns_without_np=$(comm -23 \
  <(kubectl get ns -o jsonpath='{.items[*].metadata.name}' | tr ' ' '\n' | sort) \
  <(kubectl get networkpolicy --all-namespaces -o jsonpath='{.items[*].metadata.namespace}' | tr ' ' '\n' | sort))
if [ -z "$ns_without_np" ]; then echo "ALL_NAMESPACES_HAVE_NETWORKPOLICIES"; else echo "MISSING_NETWORKPOLICIES: $ns_without_np"; fi

Automation

#!/usr/bin/env bash
# Applies a default-deny NetworkPolicy to every namespace that has none.
# Run on: any machine with kubectl access and current context set to target cluster.

set -euo pipefail

echo "[INFO] Discovering namespaces without any NetworkPolicy..."
ns_without_np=$(comm -23 \
  <(kubectl get ns -o jsonpath='{.items[*].metadata.name}' | tr ' ' '\n' | sort) \
  <(kubectl get networkpolicy --all-namespaces -o jsonpath='{.items[*].metadata.namespace}' | tr ' ' '\n' | sort) \
  || true)

if [ -z "${ns_without_np}" ]; then
  echo "[INFO] All namespaces already have at least one NetworkPolicy."
else
  echo "[INFO] Namespaces missing NetworkPolicies:"
  echo "${ns_without_np}" | sed 's/^/  - /'

  # Apply a default-deny-all NetworkPolicy in each namespace that lacks any policy.
  # This is idempotent: apply will create or update the same object safely.
  while read -r ns; do
    [ -z "${ns}" ] && continue
    echo "[INFO] Applying default-deny-all NetworkPolicy in namespace: ${ns}"

    kubectl apply -n "${ns}" -f - <<'EOF'
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress
EOF

  done <<< "${ns_without_np}"
fi

echo "[INFO] Verifying that all namespaces now have at least one NetworkPolicy..."
verify_ns_without_np=$(comm -23 \
  <(kubectl get ns -o jsonpath='{.items[*].metadata.name}' | tr ' ' '\n' | sort) \
  <(kubectl get networkpolicy --all-namespaces -o jsonpath='{.items[*].metadata.namespace}' | tr ' ' '\n' | sort) \
  || true)

if [ -z "${verify_ns_without_np}" ]; then
  echo "ALL_NAMESPACES_HAVE_NETWORKPOLICIES"
  exit 0
else
  echo "MISSING_NETWORKPOLICIES"
  echo "[WARN] The following namespaces still lack NetworkPolicies (investigate manually):"
  echo "${verify_ns_without_np}" | sed 's/^/  - /'
  exit 1
fi