Cilium's Layer 7 policy enforcement may not occur in policies with wildcarded port ranges

Impact

For users with the following configuration:

• An allow policy that selects a Layer 3 identity and a port range AND
• A Layer 7 allow policy that selects a specific port within the first policy's range

then Layer 7 enforcement would not occur for the traffic selected by the Layer 7 policy.

This issue only affects users who use Cilium's port range functionality, which was introduced in Cilium v1.16.

For reference, an example of a pair of policies that would trigger this issue is:

apiVersion: "cilium.io/v2"
kind: CiliumNetworkPolicy
metadata:
  name: "layer-3-and-4"
spec:
  endpointSelector:
    matchLabels:
      app: service
  ingress:
    - fromCIDR:
      - 192.168.60.0/24
      toPorts:
      - ports:
        - port: "80"
          endPort: 444
          protocol: TCP

and

apiVersion: "cilium.io/v2"
kind: CiliumNetworkPolicy
metadata:
  name: "layer-4-and-7"
spec:
  endpointSelector:
    matchLabels:
      app: service
  ingress:
    toPorts:
    - ports:
      - port: "80"
        protocol: TCP
      rules:
        http:
        - method: "GET"
          path: "/public"

In the above example, requests would be permitted to all HTTP paths on matching endpoints, rather than just GET requests to the /public path as intended by the layer-4-and-7 policy. In patched versions of Cilium, the layer-4-and-7 rule would take precedence over the layer-3-and-4 rule.

Patches

This issue is patched in https://github.com/cilium/cilium/pull/35150.

This issue affects Cilium v1.16 between v1.16.0 and v1.16.3 inclusive.

This issue is patched in Cilium v1.16.4.

Workarounds

Users with network policies that match the pattern described above can work around the issue by rewriting any policies that use port ranges to individually specify the ports permitted for traffic.

Acknowledgements

The Cilium community has worked together with members of Isovalent to prepare these mitigations. Special thanks to @jrajahalme for resolving this issue.