The ha-mcp OAuth consent form (beta feature) accepts a user-supplied ha url and makes a server-side HTTP request to {ha url}/api/config with no URL validation. An unauthenticated attacker can submit arbitrary URLs to perform internal network reconnaissance via an error oracle. Two additional code paths in OAuth tool calls (REST and WebSocket) are affected by the same primitive.

The primary deployment method (private URL with pre-configured HOMEASSISTANT TOKEN) is not affected.

Code path 1 — Consent form validation (reported)

When a user submits the OAuth consent form, validate ha credentials() (provider.py) makes a server-side GET request to {ha url}/api/config with no scheme, IP, or domain validation. Different exception types produce distinct error messages, creating an error oracle:

An attacker can drive the flow programmatically: register a client via open DCR (POST /register), initiate authorization, extract a txn id, and submit arbitrary ha url values. No user interaction required.

OAuth access tokens are stateless base64-encoded JSON payloads ({"ha url": "...", "ha token": "..."}). Since tokens are not signed, an attacker can forge a token with an arbitrary ha url. REST tool calls then make HTTP requests to hardcoded HA API paths on that host (/config, /states, /services, etc.). JSON responses are returned to the caller.

In practice, path control is limited — most endpoints use absolute paths that ignore the ha url path component. Useful exfiltration requires the target to return JSON at HA API paths, which is unlikely for non-HA services.

The same forged token triggers WebSocket connections to ws://{ha url}/api/websocket. The client follows the HA WebSocket handshake protocol (waits for auth required, sends auth, expects auth ok). Non-HA targets fail at the protocol level and return nothing useful. Realistic exploitation is limited to pivoting to another HA instance on the internal network.

Confirmed: Internal network reconnaissance via error oracle (all 3 code paths). An attacker can map reachable hosts and open ports from the server's network position.

OAuth mode is a beta feature, documented separately in docs/OAUTH.md and not part of the main setup instructions. The standard deployment method (pre-configured HOMEASSISTANT URL and HOMEASSISTANT TOKEN) is not affected.

Upgrade to 7.0.0