GHSA-g936-7jqj-mwv8: TSDProxy: Internal proxy auth token forwarded to backend services enables management API escalation

Description A vulnerability was discovered in TSDProxy where it forwards its internal per-process authentication token to all proxied backend services. When identityHeaders is enabled (the default), tsdproxy injects x-tsdproxy-auth-token into every upstream HTTP request alongside user identity headers. This token is the same secret used by the management HTTP server to trust forwarded Tailscale identity claims. A backend that receives this token can replay it from localhost to the management port with an arbitrary x-tsdproxy-id value, bypassing Tailscale authentication entirely. The token is forwarded unconditionally: ProviderUserMiddleware always calls WhoisNewContext regardless of whether the user is authenticated. In the ReverseProxy.Rewrite function, WhoisFromContext returns ok=true even for zero-value Whois{} (unauthenticated or Funnel requests). The HeaderAuthToken is set for every request when identityHeaders=true. The attack requires the backend to reach 127.0.0.1:8080. This holds in: (1) non-Docker deployments where tsdproxy and a backend run on the same host, (2) Docker host-network-mode containers, (3) containers sharing tsdproxy's network namespace. Affected files - internal/proxymanager/port.go:123-132 - internal/core/admin.go:160-182 // port.go: auth token forwarded regardless of user authentication state if identityHeaders { if user, ok := model.WhoisFromContext(r.In.Context()); ok { // ok=true even for empty Whois{} stored by ProviderUserMiddleware r.Out.Header.Set(consts.HeaderAuthToken, core.ProxyAuthToken()) // token sent to backend } } // admin.go: management port trusts x-tsdproxy-id from localhost when token is valid func ResolveWhois(r *http.Request) model.Whois { if IsLocalhost(r.RemoteAddr) { return model.Whois{ ID: r.Header.Get(consts.HeaderID), // attacker-controlled after stealing token } } return model.Whois{} } Steps to reproduce 1. Deploy tsdproxy on a host (non-Docker) with a backend at http://localhost:3000. 2. Make a reques