Summary
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.
Details
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:
| Outcome |
Message returned |
Information leaked |
ConnectError |
"Could not connect..." |
Host down or port closed |
TimeoutException |
"Connection timed out..." |
Host up, port filtered |
| HTTP 401 |
"Invalid access token..." |
Service alive, requires auth |
| HTTP 403 |
"Access forbidden..." |
Service alive, forbidden |
| HTTP ≥ 400 |
"Failed to connect: HTTP {N}" |
Service alive, exact status |
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.
Code path 2 — REST tool calls with forged token
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.
Code path 3 — WebSocket tool calls with forged token
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.
Impact
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.
Scope
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.
Fix
Upgrade to 7.0.0
References
yotampe-pluto Reporter
julienld Remediation developer
Summary
The ha-mcp OAuth consent form (beta feature) accepts a user-supplied
ha_urland makes a server-side HTTP request to{ha_url}/api/configwith 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.Details
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/configwith no scheme, IP, or domain validation. Different exception types produce distinct error messages, creating an error oracle:ConnectErrorTimeoutExceptionAn attacker can drive the flow programmatically: register a client via open DCR (
POST /register), initiate authorization, extract atxn_id, and submit arbitraryha_urlvalues. No user interaction required.Code path 2 — REST tool calls with forged token
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 arbitraryha_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_urlpath component. Useful exfiltration requires the target to return JSON at HA API paths, which is unlikely for non-HA services.Code path 3 — WebSocket tool calls with forged token
The same forged token triggers WebSocket connections to
ws://{ha_url}/api/websocket. The client follows the HA WebSocket handshake protocol (waits forauth_required, sendsauth, expectsauth_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.Impact
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.
Scope
OAuth mode is a beta feature, documented separately in
docs/OAUTH.mdand not part of the main setup instructions. The standard deployment method (pre-configuredHOMEASSISTANT_URLandHOMEASSISTANT_TOKEN) is not affected.Fix
Upgrade to 7.0.0
References