Summary

The Fission router registers an internal-style route — /fission-function/<name> and
/fission-function/<ns>/<name> — for every Function object, independent of whether any
HTTPTrigger exists for that function. The route was mounted on the same listener as
user-defined HTTPTriggers (svc/router, port 8888), so any caller who could reach the router
could invoke any function by guessing its metadata.name (and namespace), bypassing the host /
path / method / method-allow-list restrictions encoded in HTTPTrigger objects.

Affected component

• pkg/router/httpTriggers.go:280-284 — internalRoute registration via
  utils.UrlForFunction(fn.Name, fn.Namespace), bound to the function handler.

Impact

An external caller who reaches the public router could:

1. Invoke functions that the operator intentionally did not publish through an HTTPTrigger
   (e.g. functions used only as Kubewatcher / Timer / MessageQueue trigger targets, internal
   helpers, or sample functions).
2. Bypass HTTPTrigger-level restrictions: a function published only on POST /api/v2/foo
   could still be invoked as GET /fission-function/<ns>/<name> with arbitrary headers and body.
3. Enumerate function names by probing the response semantics (404 vs 200 vs 502 from cold
   start).

In multi-tenant deployments this also crosses tenant boundaries when functions in tenant
namespace B are reachable from tenant A's pods (or from anywhere on the internet if the router
is ingress-exposed).

Root cause

/fission-function/... was historically used by internal trigger sources (timer, kubewatcher,
mqtrigger) that share the cluster network with the router, but the route was registered on the
public listener that also serves user HTTPTriggers. The two audiences were never separated.

Fix

Released in v1.23.0:

• PR #3369 (commit 814d232c): the router now runs two listeners — a public listener
  (port 8888, svc/router) that serves only user-defined HTTPTriggers, /router-healthz, and
  /_version, and an internal listener (port 8889, svc/router-internal, ClusterIP-only) that
  exclusively serves /fission-function/<ns>/<name>. The internal listener is wrapped with the
  pkg/auth/hmac.ServiceVerifier using the ServiceRouterInternal derived key — internal trigger
  sources sign their requests with a per-service HKDF-derived key from a cluster master secret.
  Empty master secret falls back to pass-through (preserves compatibility for clusters not yet
  rotating in a secret).
• PR #3365 (commit 0aa24788): added per-service NetworkPolicy resources to
  charts/fission-all, ensuring svc/router-internal is only reachable from kubewatcher,
  timer, mqtrigger, and mqt-keda pods inside the release namespace.
• The internal-listener path itself is still /fission-function/<ns>/<name> — only its
  location moved.

Mitigation (until upgrade)

1. Apply a NetworkPolicy to the Fission namespace that allows ingress to svc/router (port

8888. only from your ingress controller, and blocks /fission-function/... at the ingress layer
      (path-based filter on the ingress).

2. Avoid exposing the router directly via LoadBalancer/NodePort; front it with an ingress that
   path-filters /fission-function/.
3. Treat function metadata.name as not a secret — names should not be the access control
   boundary.