CVE-2026-54246: Github.com/zalando/skipper All Routesrv API Endpoints Lack Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5587-2x54-jj6h",
  "modified" : "2026-07-17T21:46:18Z",
  "published" : "2026-07-17T21:46:18Z",
  "aliases" : [ "CVE-2026-54246" ],
  "summary" : "Skipper's routesrv-no-auth component: All routesrv API Endpoints Lack Authentication",
  "details" : "## Description\n\nThe `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.\n\n## Vulnerable Code\n\n**routesrv/routesrv.go:87-99,114-137** — all handler registrations on the main mux:\n```go\nmux.Handle(\"/routes\", b)          // eskipBytes.ServeHTTP — all route data\nmux.Handle(\"/routes/{zone}\", b)   // zone-scoped route data\nmux.Handle(\"/swarm/redis/shards\", rh)   // Redis cluster addresses\nmux.Handle(\"/swarm/valkey/shards\", vh)  // Valkey cluster addresses\n```\n\n**routesrv/eskipbytes.go:134-196** — `eskipBytes.ServeHTTP`:\n```go\nfunc (e *eskipBytes) ServeHTTP(rw http.ResponseWriter, r *http.Request) {\n    // ... only checks GET/HEAD method, NO auth check\n    if r.Method != \"GET\" && r.Method != \"HEAD\" {\n        w.WriteHeader(http.StatusMethodNotAllowed)\n        return\n    }\n    // ... serves all route data immediately\n}\n```\n\n**routesrv/redishandler.go:28-41** — `RedisHandler.ServeHTTP`:\n```go\nfunc (rh *RedisHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {\n    if r.Method != \"GET\" {\n        w.WriteHeader(http.StatusMethodNotAllowed)\n        return\n    }\n    // ... serves Redis cluster addresses immediately, NO auth check\n}\n```\n\n**routesrv/valkeyhandler.go:28-41** — `ValkeyHandler.ServeHTTP`:\n```go\nfunc (vh *ValkeyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {\n    if r.Method != \"GET\" {\n        w.WriteHeader(http.StatusMethodNotAllowed)\n        return\n    }\n    // ... serves Valkey cluster addresses immediately, NO auth check\n}\n```\n\n## Attack Path\n\n1. **Initial Compromise**: Attacker compromises any pod in the Kubernetes cluster (via application CVE, supply-chain attack, malicious container image, etc.)\n2. **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`)\n3. **Data Extraction without Auth**: \n   - `GET http://<routesrv>:9090/routes` → All Ingress/RouteGroup configurations across ALL namespaces\n   - `GET http://<routesrv>:9090/swarm/redis/shards` → Redis cache cluster node addresses\n   - `GET http://<routesrv>:9090/swarm/valkey/shards` → Valkey cache cluster node addresses\n4. **Subsequent Attacks**: With cache cluster topology, attacker can perform direct cache-level attacks (ratelimit data manipulation, session data exfiltration)\n\n## Permission Boundary Analysis\n\nThe 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**.\n\nA 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\"*.\n\nNo 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.\n\n## Exposed Data\n\n| Endpoint | Data Exposed | Impact |\n|----------|-------------|--------|\n| `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 |\n| `GET /routes/{zone}` | Zone-scoped subset of above route data | Same, scoped |\n| `GET /swarm/redis/shards` | Redis cluster internal IP:port pairs | Direct cache-level attacks, ratelimit data manipulation |\n| `GET /swarm/valkey/shards` | Valkey cluster internal IP:port pairs | Same |\n\nAdditionally, 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.\n\n\n## Mitigation\n\n1. Add authentication to all routesrv HTTP endpoints (basic auth, bearer token, mTLS, or shared secret) via flag `-route-server-filters=\"\"`\n2. Deploy Kubernetes NetworkPolicies restricting ingress to routesrv to only the data-plane skipper pod selectors\n3. Consider using mutual TLS authentication between data-plane and control-plane components\n\n\n### NetworkPolicy does not remove the missing-auth condition\nRestrictive 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.\n\n### Impact framing\nThis 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.\n\n## Resources\n\n- `routesrv/routesrv.go:87-99` — handler registration (zero auth)\n- `routesrv/eskipbytes.go:134-196` — route data handler (no auth)\n- `routesrv/redishandler.go:28-41` — Redis shard handler (no auth)\n- `routesrv/valkeyhandler.go:28-41` — Valkey shard handler (no auth)\n- `dataclients/kubernetes/clusterclient.go:648-653` — `fetchClusterState()` — shows cluster-wide RBAC\n- `eskipfile/remote.go:190-219` — data-plane client also has no auth capability\n- `docs/tutorials/operations.md:108`, `docs/tutorials/ratelimit.md:137,197` — documented routesrv DNS name",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/zalando/skipper"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.27.13"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/zalando/skipper/security/advisories/GHSA-5587-2x54-jj6h"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/zalando/skipper"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zalando/skipper/releases/tag/v0.27.13"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-306" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-17T21:46:18Z",
    "nvd_published_at" : null
  }
}