Cilium Network Policy Review
Purpose
Review Cilium policy resources against zero-trust correctness, blast radius, and the operational traps unique to eBPF-backed networking. Cilium's policy surface is broader than native Kubernetes NetworkPolicy - CiliumNetworkPolicy adds L7 rules, FQDN matching, ICMP control, and identity-based selectors; CiliumClusterwideNetworkPolicy applies cluster-wide; CiliumEgressGatewayPolicy controls SNAT egress IPs; and policy-default-local-cluster changes how policy evaluates across ClusterMesh.
Lean operating rules
- Prefer live cluster evidence (
kubectl get networkpolicies,ciliumnetworkpolicies,ciliumclusterwidenetworkpolicies,ciliumegressgatewaypolicies -A -o yaml, cilium policy get, cilium clustermesh inspect-policy-default-local-cluster, and Hubble flow observation) when the active client exposes it; otherwise fall back to official Cilium documentation (docs.cilium.io) and sanitized YAML.
- Separate confirmed facts from inference. If Cilium agent state, ClusterMesh peer status, or Hubble flow data was not queried, say so.
- Treat removal of a default-deny
NetworkPolicy in a namespace as a critical finding - pods become reachable from any source/destination unless another policy provides isolation.
- Treat
CiliumNetworkPolicy egress with toCIDRSet: [{cidr: 0.0.0.0/0}] (no except for sensitive CIDRs) as a critical finding - unrestricted egress is a documented data exfiltration path.
- Treat any change to
policy-default-local-cluster in a ClusterMesh deployment as critical-blast-radius - every existing policy's cross-cluster semantics flip simultaneously.
- Challenge
CiliumEgressGatewayPolicy with the same egressIP used in two policies - silent connection breakage when both match.
- Challenge L7 rules in
CiliumNetworkPolicy for namespaces where Envoy proxy is not enabled - L7 fields require the proxy.
- Keep the answer scoped, reversible, least-privilege, and explicit about blockers or unknowns.
References
Load these only when needed:
- Evidence path and tooling - use when choosing live cluster evidence, confirming Cilium version and ClusterMesh state, or switching to documentation mode.
- Workflow and output contract - use when executing the full review, applying stress checks across the three policy formats and ClusterMesh, or formatting the final answer.
- Official sources - use when you need the detailed Cilium documentation list, CRD schema, and grounded insights.
Response minimum
Return, at minimum:
- the scoped target (namespace
NetworkPolicy, namespace CiliumNetworkPolicy, cluster-wide CiliumClusterwideNetworkPolicy, CiliumEgressGatewayPolicy) and evidence level,
- the default-deny posture in the affected namespace(s),
- the L7 enforcement assessment (Envoy proxy enabled / required) and whether L7 rules will actually run,
- the ClusterMesh assessment when applicable (
policy-default-local-cluster semantics),
- the safest next actions and rollback plan,
- the assumptions or blockers that prevent stronger conclusions.
1---2name: techtide-cilium-network-policy-review3description: Use this skill for Cilium network policy review across the three policy formats (Kubernetes NetworkPolicy, CiliumNetworkPolicy, CiliumClusterwideNetworkPolicy), L7 policy via embedded Envoy, ClusterMesh cross-cluster semantics, Hubble flow observability, and CiliumEgressGatewayPolicy. Trigger when the user asks whether a network policy is too broad, whether default-deny is in place, whether L7 rules will actually be enforced, whether ClusterMesh policy semantics are correct, or whether an egress gateway IP collision is possible.4---56# Cilium Network Policy Review78## Purpose910Review Cilium policy resources against zero-trust correctness, blast radius, and the operational traps unique to eBPF-backed networking. Cilium's policy surface is broader than native Kubernetes NetworkPolicy - `CiliumNetworkPolicy` adds L7 rules, FQDN matching, ICMP control, and identity-based selectors; `CiliumClusterwideNetworkPolicy` applies cluster-wide; `CiliumEgressGatewayPolicy` controls SNAT egress IPs; and `policy-default-local-cluster` changes how policy evaluates across ClusterMesh.1112## Lean operating rules1314- Prefer live cluster evidence (`kubectl get networkpolicies,ciliumnetworkpolicies,ciliumclusterwidenetworkpolicies,ciliumegressgatewaypolicies -A -o yaml`, `cilium policy get`, `cilium clustermesh inspect-policy-default-local-cluster`, and Hubble flow observation) when the active client exposes it; otherwise fall back to official Cilium documentation (docs.cilium.io) and sanitized YAML.15- Separate confirmed facts from inference. If Cilium agent state, ClusterMesh peer status, or Hubble flow data was not queried, say so.16- Treat **removal of a default-deny `NetworkPolicy`** in a namespace as a critical finding - pods become reachable from any source/destination unless another policy provides isolation.17- Treat `CiliumNetworkPolicy` egress with `toCIDRSet: [{cidr: 0.0.0.0/0}]` (no `except` for sensitive CIDRs) as a critical finding - unrestricted egress is a documented data exfiltration path.18- Treat any change to `policy-default-local-cluster` in a ClusterMesh deployment as critical-blast-radius - every existing policy's cross-cluster semantics flip simultaneously.19- Challenge `CiliumEgressGatewayPolicy` with the same `egressIP` used in two policies - silent connection breakage when both match.20- Challenge L7 rules in `CiliumNetworkPolicy` for namespaces where Envoy proxy is not enabled - L7 fields require the proxy.21- Keep the answer scoped, reversible, least-privilege, and explicit about blockers or unknowns.2223## References2425Load these only when needed:2627- [Evidence path and tooling](references/mcp-and-evidence.md) - use when choosing live cluster evidence, confirming Cilium version and ClusterMesh state, or switching to documentation mode.28- [Workflow and output contract](references/workflow-and-output.md) - use when executing the full review, applying stress checks across the three policy formats and ClusterMesh, or formatting the final answer.29- [Official sources](references/official-sources.md) - use when you need the detailed Cilium documentation list, CRD schema, and grounded insights.3031## Response minimum3233Return, at minimum:3435- the scoped target (namespace `NetworkPolicy`, namespace `CiliumNetworkPolicy`, cluster-wide `CiliumClusterwideNetworkPolicy`, `CiliumEgressGatewayPolicy`) and evidence level,36- the default-deny posture in the affected namespace(s),37- the L7 enforcement assessment (Envoy proxy enabled / required) and whether L7 rules will actually run,38- the ClusterMesh assessment when applicable (`policy-default-local-cluster` semantics),39- the safest next actions and rollback plan,40- the assumptions or blockers that prevent stronger conclusions.
TechTideOhio