{"id":"GHSA-g936-7jqj-mwv8","title":"TSDProxy: Internal proxy auth token forwarded to backend services enables management API escalation","summary":"TSDProxy: Internal proxy auth token forwarded to backend services enables management API escalation","severity":"critical","cvss":9,"cwe":["CWE-200","CWE-287"],"vendor":"almeidapaulopt","product":"github.com/almeidapaulopt/tsdproxy","ecosystem":"go","affected":["github.com/almeidapaulopt/tsdproxy < 1.4.4-0.20260603142855-434819b4421e"],"patched":["github.com/almeidapaulopt/tsdproxy 1.4.4-0.20260603142855-434819b4421e"],"published":"2026-07-10","updated":"2026-07-10","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-g936-7jqj-mwv8","references":[{"url":"https://github.com/almeidapaulopt/tsdproxy/security/advisories/GHSA-g936-7jqj-mwv8"},{"url":"https://github.com/advisories/GHSA-g936-7jqj-mwv8"}],"tags":["ghsa","go"],"ingestedAt":"2026-07-10T22:06:49.342Z","slug":"GHSA-g936-7jqj-mwv8","body":"## Overview\n\n## Description\n\nA 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.\n\nThe 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`.\n\nThe 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.\n\n## Affected files\n\n- `internal/proxymanager/port.go:123-132`\n- `internal/core/admin.go:160-182`\n\n```go\n// port.go: auth token forwarded regardless of user authentication state\nif identityHeaders {\n    if user, ok := model.WhoisFromContext(r.In.Context()); ok {\n        // ok=true even for empty Whois{} stored by ProviderUserMiddleware\n        r.Out.Header.Set(consts.HeaderAuthToken, core.ProxyAuthToken()) // token sent to backend\n    }\n}\n\n// admin.go: management port trusts x-tsdproxy-id from localhost when token is valid\nfunc ResolveWhois(r *http.Request) model.Whois {\n    if IsLocalhost(r.RemoteAddr) {\n        return model.Whois{\n            ID: r.Header.Get(consts.HeaderID), // attacker-controlled after stealing token\n        }\n    }\n    return model.Whois{}\n}\n```\n\n## Steps to reproduce\n\n1. Deploy tsdproxy on a host (non-Docker) with a backend at `http://localhost:3000`.\n2. Make a request through the Tailscale proxy. The backend receives `x-tsdproxy-auth-token` in the request headers.\n3. From the host, replay the token to the management API:\n\n```bash\n# Capture token from backend headers (e.g., via a header-reflection endpoint)\nTOKEN=$(curl -s http://localhost:3000/debug/headers | python3 -c \"import sys,json; d=json.load(sys.stdin); print(d['headers'].get('X-Tsdproxy-Auth-Token',''))\")\n\n# Replay from localhost to gain admin access\ncurl -H \"x-tsdproxy-auth-token: $TOKEN\" \\\n     -H \"x-tsdproxy-id: attacker\" \\\n     http://127.0.0.1:8080/api/v1/proxies\n# Returns full proxy list with admin access\n```\n\n## Fix\n\nRemove `HeaderAuthToken` from the outgoing backend request, and guard identity-header injection on `user.ID != \"\"`:\n\n```go\n// port.go: only inject headers for actually authenticated users\nif identityHeaders {\n    if user, ok := model.WhoisFromContext(r.In.Context()); ok && user.ID != \"\" {\n        r.Out.Header.Set(consts.HeaderID, user.ID)\n        // HeaderAuthToken should NOT be forwarded to backends\n    }\n}\n```\n\n## Impact\n\nAn attacker with code execution in any backend proxied by tsdproxy (on the same host) gains full management API control: restart or pause all proxied services (DoS), enumerate all proxy configurations and backend network topology, and trigger webhook deliveries (SSRF via configured webhook URLs).\n\n## Credits\n\nReported by Vishal Shukla (@shukla304 / @therawdev).\n\n## Sponsorship\n\nThis audit is from an AI-assisted research agent at [sechub.dev](https://sechub.dev). Running it on OSS projects is free for maintainers.\n\n## Affected packages\n\n- `github.com/almeidapaulopt/tsdproxy < 1.4.4-0.20260603142855-434819b4421e`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `github.com/almeidapaulopt/tsdproxy 1.4.4-0.20260603142855-434819b4421e`","depth":"midnight","depthScore":50,"depthScoreParts":{"impact":49.5,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}