GHSA-5587-2x54-jj6h Skipper's routesrv-no-auth component: All routesrv API Endpoints Lack Authentication

• Go github.com/zalando/skipper: < 0.27.13 → fixed in 0.27.13

Description The `routesrv` component exposes the full cluster route topology (Ingress/RouteGroup configurations, backend URLs, filter chains, OAuth/OIDC callback paths) and cache-cluster topology (Redis/Valkey shard addresses) over plain HTTP with zero authentication. Any pod in the Kubernetes cluster can reach routesrv via its predictable DNS name and retrieve sensitive cluster-wide routing and cache infrastructure data. Vulnerable Code routesrv/routesrv.go:87-99,114-137 — all handler registrations on the main mux: ```go mux.Handle("/routes", b) // eskipBytes.ServeHTTP — all route data mux.Handle("/routes/{zone}", b) // zone-scoped route data mux.Handle("/swarm/redis/shards", rh) // Redis cluster addresses mux.Handle("/swarm/valkey/shards", vh) // Valkey cluster addresses ``` routesrv/eskipbytes.go:134-196 — `eskipBytes.ServeHTTP`: ```go func (e *eskipBytes) ServeHTTP(rw http.ResponseWriter, r *http.Request) { // ... only checks GET/HEAD method, NO auth check if r.Method != "GET" && r.Method != "HEAD" { w.WriteHeader(http.StatusMethodNotAllowed) return } // ... serves all route data immediately } ``` routesrv/redishandler.go:28-41 — `RedisHandler.ServeHTTP`: ```go func (rh *RedisHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) { if r.Method != "GET" { w.WriteHeader(http.StatusMethodNotAllowed) return } // ... serves Redis cluster addresses immediately, NO auth check } ``` routesrv/valkeyhandler.go:28-41 — `ValkeyHandler.ServeHTTP`: ```go func (vh *ValkeyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) { if r.Method != "GET" { w.WriteHeader(http.StatusMethodNotAllowed) return } // ... serves Valkey cluster addresses immediately, NO auth check } ``` Attack Path 1. Initial Compromise: Attacker compromises any pod in the Kubernetes cluster (via application CVE, supply-chain attack, malicious container image, etc.) 2. Discovery: Attacker discovers routesrv via predictable Kubernetes DNS name: `skipper-ingress-routesrv.kube-system.svc.cluster.local:9090` (documented at `docs/tutorials/operations.md:108`, `docs/tutorials/ratelimit.md:137,197`) 3. Data Extraction without Auth: • `GET http://:9090/routes` → All Ingress/RouteGroup configurations across ALL namespaces • `GET http://:9090/swarm/redis/shards` → Redis cache cluster node addresses • `GET http://:9090/swarm/valkey/shards` → Valkey cache cluster node addresses 4. Subsequent Attacks: With cache cluster topology, attacker can perform direct cache-level attacks (ratelimit data manipulation, session data exfiltration) Permission Boundary Analysis The routesrv uses a ServiceAccount with cluster-wide RBAC to list Ingress (networking.k8s.io), RouteGroup (zalando.org), Endpoints, and Services across all namespaces (see `clusterclient.go:648-653` `fetchClusterState`). The kube-apiserver requires proper ServiceAccount token + RBAC authorization for the Kubernetes API itself, but routesrv exposes the aggregated data over HTTP with zero authentication. A compromised pod with limited RBAC (restricted to its own namespace) can bypass Kubernetes RBAC entirely by reading routesrv. This crosses the boundary from *"namespace-scoped Kubernetes workload with restricted RBAC"* to *"full cluster route topology across all namespaces"*. No NetworkPolicy manifests exist in the `deploy/` directory. The default Kubernetes flat network model allows any pod to reach any service, further widening the attack surface. Exposed Data | Endpoint | Data Exposed | Impact | |----------|-------------|--------| | `GET /routes` | All ingress/routegroup backends: internal service URLs, filter chains (auth, rate limiting, OAuth, JWT, OPA policies), load balancer group membership | Cluster-wide reconnaissance, targeted backend attacks | | `GET /routes/{zone}` | Zone-scoped subset of above route data | Same, scoped | | `GET /swarm/redis/shards` | Redis cluster internal IP:port pairs | Direct cache-level attacks, ratelimit data manipulation | | `GET /swarm/valkey/shards` | Valkey cluster internal IP:port pairs | Same | Additionally, the data-plane client (`eskipfile/remote.go:190-219`) also performs plain HTTP GET with no credentials — only an ETag header is sent — confirming that no auth capability exists in the architecture at all. Mitigation 1. Add authentication to all routesrv HTTP endpoints (basic auth, bearer token, mTLS, or shared secret) via flag `-route-server-filters=""` 2. Deploy Kubernetes NetworkPolicies restricting ingress to routesrv to only the data-plane skipper pod selectors 3. Consider using mutual TLS authentication between data-plane and control-plane components NetworkPolicy does not remove the missing-auth condition Restrictive NetworkPolicies are a valid mitigation, but they are not an application-layer authentication mechanism. The security-relevant defect remains that routesrv serves control-plane-derived data to unauthenticated callers whenever network reachability exists. Impact framing This report does not rely on claiming direct integrity or availability impact. The verified issue is a confidentiality-focused control-plane exposure: route definitions, backend topology, filter-chain details, and Redis/Valkey shard addresses become readable to any reachable in-cluster client. Resources • `routesrv/routesrv.go:87-99` — handler registration (zero auth) • `routesrv/eskipbytes.go:134-196` — route data handler (no auth) • `routesrv/redishandler.go:28-41` — Redis shard handler (no auth) • `routesrv/valkeyhandler.go:28-41` — Valkey shard handler (no auth) • `dataclients/kubernetes/clusterclient.go:648-653` — `fetchClusterState()` — shows cluster-wide RBAC • `eskipfile/remote.go:190-219` — data-plane client also has no auth capability • `docs/tutorials/operations.md:108`, `docs/tutorials/ratelimit.md:137,197` — documented routesrv DNS name