GHSA-g936-7jqj-mwv8: TSDProxy Internal Proxy Auth Token Forwarded Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g936-7jqj-mwv8",
  "modified" : "2026-07-10T21:43:13Z",
  "published" : "2026-07-10T21:43:13Z",
  "aliases" : [ ],
  "summary" : "TSDProxy: Internal proxy auth token forwarded to backend services enables management API escalation",
  "details" : "## 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/almeidapaulopt/tsdproxy"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.4.4-0.20260603142855-434819b4421e"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/almeidapaulopt/tsdproxy/security/advisories/GHSA-g936-7jqj-mwv8"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/almeidapaulopt/tsdproxy"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-200", "CWE-287" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-10T21:43:13Z",
    "nvd_published_at" : null
  }
}