GHSA-94f4-hr76-p5j6 vLLM: OpenAI auth bypass

• PyPI vllm: >= 0.3.0, < 0.22.0 → fixed in 0.22.0

Summary A vulnerability in ASGI web servers and starlette's trust on those web servers enables an authentication bypass of the OpenAI API `AuthenticationMiddleware`, which was discovered during @x41sec's source code audit. It allows to use the API without providing the configured `VLLM_API_KEY` or `--api-key`. Details In https://github.com/vllm-project/vllm/blob/v0.14.0/vllm/entrypoints/openai/api_server.py#L689-L692 the `url_path` is taken from the `URL`, which is reconstructed by _starlette_ based on the request `scope`. ```py from starlette.datastructures import URL, Headers, MutableHeaders, State ... url_path = URL(scope=scope).path.removeprefix(root_path) headers = Headers(scope=scope) if url_path.startswith("/v1") and not self.verify_token(headers): response = JSONResponse(content={"error": "Unauthorized"}, status_code=401) return response(scope, receive, send) return self.app(scope, receive, send) ``` The request `scope` includes the request's `Host:` header and reconstructs the URL as shown below: ```py f"{scheme}://{host_header}{path}" ``` Neither starlette nor any of the ASGI servers (including uvicorn, which vllm uses) properly filter the `Host:` header for invalid characters. This allows an attacker to include special URL characters such as `/` or `?` in the `Host:` header and thereby control the reconstructed URL and it's `.path` attribute. FastAPI/starlette's routing uses the HTTP path and does not depend on the parsed url.path attribute, allowing attackers to reach an endpoint via a certain path while providing a different value in the `.path`. Impact • Instances of vllm that use an API Key for the OpenAI API and expose the API to attackers. • Instances behind an RFC-conforming web server (such as nginx) are not affected.