GHSA-g936-7jqj-mwv8

## 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` ```go // 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