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A high-severity vulnerability in Traefik's Kubernetes Gateway provider allows bypass of the crossProviderNamespaces allowlist when processing HTTPRoute rules that contain multiple backendRefs. Due to incorrect enforcement of namespace restrictions in this code path, a route originating from a non-allowlisted namespace can reference and expose internal Traefik services such as api@internal, dashboard@internal, or rest@internal, provided the route is accepted and a matching ReferenceGrant from an allow-listed namespace can be leveraged. The issue undermines the intended namespace-based isolation enforced by crossProviderNamespaces.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository is a small, self-contained proof-of-concept for CVE-2026-54761 affecting Traefik's Kubernetes Gateway provider. It is not a general exploit framework module; instead it builds a disposable local kind-based Kubernetes lab to reproduce an authorization bypass involving `crossProviderNamespaces` validation. Repository structure: - `README.md`: documents the vulnerability, affected/fixed versions, expected behavior, and how to run the PoC. - `external-repro-kind/run-kind-repro.sh`: main entry point. It validates dependencies, creates/deletes a kind cluster, pulls Traefik and whoami images, installs Gateway API CRDs from GitHub, deploys vulnerable Traefik, applies the exploit manifests, and verifies both the control and exploit routes with curl. - `external-repro-kind/kind-config.yaml`: exposes the cluster service locally by mapping NodePort 30080 to `127.0.0.1:18080`. - `external-repro-kind/traefik-v371.yaml`: deploys Traefik v3.7.1 with `--providers.kubernetesgateway=true` and `--providers.kubernetesgateway.crossprovidernamespaces=trusted`, plus RBAC, ServiceAccount, NodePort service, and GatewayClass. - `external-repro-kind/gateway-exploit.yaml`: defines namespaces `attacker` and `trusted`, a benign `whoami` service, a `ReferenceGrant`, a shared Gateway, a single-backend control `HTTPRoute`, and the malicious weighted-backend `HTTPRoute`. Exploit capability: The exploit demonstrates that an `HTTPRoute` in an untrusted namespace (`attacker`) can still expose Traefik internal services when it uses multiple weighted backend references and points the `TraefikService` backend at an allow-listed namespace (`trusted`). The control route (`control.localhost`) uses a single forbidden backend reference and should return 404. The exploit route (`exploit.localhost`) uses two backends, heavily weighting `api@internal`, and on vulnerable versions causes requests to `/api/http/services` to return Traefik API JSON. This confirms unauthorized exposure of internal control-plane functionality through the normal HTTP data plane. Overall, this is a legitimate local PoC exploit for a Kubernetes/Gateway API misconfiguration and validation flaw. It does not deliver code execution or a shell; its purpose is to prove unauthorized access to internal Traefik services under specific vulnerable routing conditions.
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