Network Security & LAN Isolation

This document details the Cilium network policy that isolates Kubernetes pods from the local network, preventing lateral movement attacks while allowing legitimate traffic.

Overview

The cluster uses a CiliumClusterwideNetworkPolicy to implement a "default deny" stance for LAN access. This provides an 80/20 security solution - one policy that protects all pods without requiring per-app network policies.

The Threat Model

When hosting public-facing applications (via Cloudflare Tunnel), an attacker who exploits a vulnerability could:

1. Gain shell access inside a pod
2. Scan the internal network
3. Pivot to attack other LAN devices (router, NAS, other servers)

graph LR
    subgraph "Internet"
        Attacker[Attacker]
    end

    subgraph "Cloudflare"
        CF[Cloudflare Tunnel]
    end

    subgraph "Kubernetes Cluster"
        VulnPod[Vulnerable Pod]
    end

    subgraph "LAN (192.168.10.0/24)"
        Router[Router .1]
        NAS[TrueNAS .133]
        Other[Other Devices]
    end

    Attacker -->|1. Exploit| CF
    CF -->|2. RCE| VulnPod
    VulnPod -.->|3. Pivot BLOCKED| Router
    VulnPod -.->|3. Pivot BLOCKED| Other

    style VulnPod fill:#f96,stroke:#333,stroke-width:2px
    style Router fill:#f66,stroke:#333,stroke-width:2px

The Solution: CiliumClusterwideNetworkPolicy

Located at: infrastructure/networking/cilium/policies/block-lan-access.yaml

What Gets Blocked

What Gets Allowed

Policy Architecture

graph TD
    subgraph "Egress Rules"
        Internet[Internet
0.0.0.0/0 EXCEPT RFC1918]
        Cluster[Cluster Entities
pods, nodes, apiserver]
        Storage[Whitelisted Storage
TrueNAS: NFS,SMB,RustFS]
        LB[LoadBalancer Pool
192.168.10.32/27]
    end

    subgraph "All Pods"
        Pod[Any Pod]
    end

    subgraph "Blocked"
        LAN[LAN Devices
192.168.10.x]
        Router[Router
192.168.10.1]
    end

    Pod -->|ALLOWED| Internet
    Pod -->|ALLOWED| Cluster
    Pod -->|ALLOWED| Storage
    Pod -->|ALLOWED| LB
    Pod -.->|BLOCKED| LAN
    Pod -.->|BLOCKED| Router

    style LAN fill:#f66,stroke:#333
    style Router fill:#f66,stroke:#333
    style Internet fill:#6f6,stroke:#333
    style Cluster fill:#6f6,stroke:#333

Whitelisted LAN Resources

These specific IPs are allowed on specific ports only:

Why Lateral Movement Fails

The policy uses endpointSelector: {} which matches ALL pods in the cluster:

spec:
  endpointSelector: {}  # <-- Applies to EVERY pod

This means: - DVWA pod cannot reach LAN - n8n pod cannot reach LAN - If attacker pivots from DVWA → n8n, n8n STILL cannot reach LAN

sequenceDiagram
    participant Attacker
    participant DVWA as DVWA Pod
    participant N8N as n8n Pod
    participant Router as Router (192.168.10.1)

    Attacker->>DVWA: Exploit vulnerability
    Note over DVWA: Shell access gained

    DVWA->>Router: ping 192.168.10.1
    Router--xDVWA: BLOCKED (100% packet loss)

    DVWA->>N8N: Pivot to n8n pod
    Note over N8N: Lateral movement works

    N8N->>Router: ping 192.168.10.1
    Router--xN8N: STILL BLOCKED

    Note over Attacker,Router: No matter which pod,
LAN is unreachable

Testing the Policy

Quick Test (from any pod)

# Test LAN access (should fail)
kubectl exec -n <namespace> <pod> -- ping -c 1 -W 2 192.168.10.1

# Test internet access (should work)
kubectl exec -n <namespace> <pod> -- ping -c 2 8.8.8.8

Full Pentest Simulation

Deploy DVWA (Damn Vulnerable Web Application) for realistic testing:

1. Access https://dvwa.vanillax.me
2. Login: admin / password
3. Set security to "Low"
4. Navigate to Command Injection
5. Try: ; ping -c 1 -W 2 192.168.10.1

Expected Result: 100% packet loss (LAN blocked)

Verify from Multiple Pods

# Test from different namespaces
for ns in dvwa n8n immich; do
  echo "=== Testing from $ns ==="
  kubectl exec -n $ns deploy/${ns} -- ping -c 1 -W 2 192.168.10.1 2>&1 | grep -E "packet loss|PING"
done

Hubble Observability

Use Hubble to see policy enforcement in real-time:

# Watch for dropped traffic
hubble observe --verdict DROPPED --to-ip 192.168.10.0/24

# Watch specific pod
hubble observe --pod dvwa/dvwa --verdict DROPPED

Troubleshooting

App Can't Reach Required LAN Resource

Add a specific whitelist rule:

- toCIDR:
    - 192.168.10.X/32  # The IP you need
  toPorts:
    - ports:
        - port: "XXXX"  # Only the required port
          protocol: TCP

Policy Not Taking Effect

1. Check Cilium agent is running: kubectl get pods -n kube-system -l k8s-app=cilium
2. Verify policy is applied: kubectl get ciliumclusterwidenetworkpolicies
3. Check Hubble for verdicts: hubble observe --pod <your-pod>

Internet Stopped Working

Ensure toEntities: host is present - this allows traffic to reach the node which then NATs to the internet.

Security Considerations

1. Minimize Whitelists: Only add LAN IPs that are absolutely necessary
2. Port Restrict: Always specify ports, never allow all ports to a LAN IP
3. No Router Access: Never whitelist 192.168.10.1 (your gateway)
4. Regular Audits: Review whitelisted IPs periodically