Unauthenticated HTTP MCP browser-control surface in camofox-mcp

Summary

camofox-mcp exposed a Streamable HTTP MCP endpoint at /mcp with rate limiting but no inbound MCP-layer authentication. When HTTP mode was enabled, any client that could reach /mcp could list and invoke browser-control tools.

If CAMOFOX_API_KEY was configured, the server then forwarded that server-side key to the underlying camofox-browser backend. That means an unauthenticated MCP caller could exercise the server's browser authority without knowing the backend browser API key.

Reviewed vulnerable commit: 10e3ac08cb50d830eb4ee00a789229f02f28a1a4 Fixed commit observed on main: 599f56ee40f8062aeca541c251ed1d39fb437f50 Fixed release observed: v1.13.2 Suggested severity: High, with the caveat that default loopback-only deployments reduce practical exposure.

Root cause

In the reviewed commit, src/http.ts creates the Express MCP app and applies only a rate limiter to /mcp:

const app = createMcpExpressApp({ host: config.httpHost });

const limiter = rateLimit({
  windowMs: 60_000,
  limit: config.httpRateLimit,
  standardHeaders: true,
  legacyHeaders: false
});

app.use("/mcp", limiter);

The POST /mcp handler then creates a server and StreamableHTTPServerTransport and passes the request body into the MCP transport without checking Authorization, an inbound API key, allowed hosts, or public-bind safety:

app.post("/mcp", async (req: any, res: any) => {
  try {
    const { server } = createServer(config);
    const transport = new StreamableHTTPServerTransport({ sessionIdGenerator: undefined });

    await server.connect(transport);
    await transport.handleRequest(req, res, req.body);

src/config.ts made HTTP mode configurable and defaulted the HTTP host to loopback, but it did not require an inbound HTTP client secret:

transport: cli.transport ?? envTransport ?? "stdio",
httpPort: cli.httpPort ?? (Number.isNaN(httpPortFromEnv) ? 3000 : httpPortFromEnv),
httpHost: cli.httpHost ?? env.CAMOFOX_HTTP_HOST ?? "127.0.0.1",

Separately, src/client.ts forwarded CAMOFOX_API_KEY server-side to the browser backend:

if (this.apiKey) {
  headers.set("x-api-key", this.apiKey);
  headers.set("authorization", `Bearer ${this.apiKey}`);
}

So CAMOFOX_API_KEY protected the MCP server's outbound requests to the backend browser service, but did not authenticate inbound HTTP MCP clients.

Auth boundary

The vulnerable boundary was the HTTP MCP endpoint. The client did not need to provide Authorization or any CAMOFOX_API_KEY value to call MCP tools.

The default bind was 127.0.0.1, which lowers severity for default local-only deployments. The risky cases are documented HTTP/remote-client deployments, Docker/port-forwarded deployments, or any environment where a browser page, local network client, reverse proxy, or another user can reach the /mcp endpoint.

Proof of concept

I used a fake camofox-browser backend so no real browser was launched and no external navigation occurred. The harness starts the reviewed dist/http.js server with CAMOFOX_API_KEY=server-side-secret, connects an MCP SDK client to /mcp with no auth headers, lists tools, then calls create_tab and navigate.

Observed output:

{
  "authUsedByClient": false,
  "listedToolCount": 46,
  "backendRequests": [
    {
      "method": "POST",
      "url": "/tabs",
      "headers": {
        "authorization": "Bearer server-side-secret",
        "x-api-key": "server-side-secret"
      }
    },
    {
      "method": "POST",
      "url": "/tabs/fake-tab-1/navigate",
      "headers": {
        "authorization": "Bearer server-side-secret",
        "x-api-key": "server-side-secret"
      }
    }
  ],
  "observedUnauthenticatedBrowserControl": true,
  "serverSideSecretForwardedToBackend": true
}

This demonstrates both parts of the issue:

1. The MCP client used no inbound authentication.
2. The server still used its configured backend browser secret when forwarding the tool calls.

Impact

An unauthenticated client that can reach the HTTP MCP endpoint can exercise browser-control tools as the MCP server. Depending on the user's active browser profiles and configured backend, that can allow page navigation, tab creation, interaction with authenticated browser contexts, screenshot/content observation, and other browser-automation actions exposed by the MCP tool surface.

The impact is strongest when HTTP mode is intentionally exposed for remote MCP clients or through Docker/reverse-proxy deployment and the operator assumes CAMOFOX_API_KEY protects the whole control plane.

Fix notes

The public issue indicates this has been fixed in 599f56e and released as v1.13.2 by adding dedicated inbound CAMOFOX_HTTP_API_KEY Bearer auth, public-bind startup validation, auth before /mcp JSON parsing, loopback Host-header protection, and optional allowed-hosts handling. Those are the right mitigation directions.