ha-mcp OAuth 2.1 DCR mode enables network reconnaissance via an error oracleGHSA-fmfg-9g7c-3vq7
MEDIUMGHSA-fmfg-9g7c-3vq7 is a medium-severity (CVSS 5.3) Server-Side Request Forgery (SSRF) vulnerability in ha-mcp. A fix is available for ha-mcp — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-fmfg-9g7c-3vq7.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
ha-mcpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | ha-mcp | all versions | 7.0.0pip install --upgrade 'ha-mcp==7.0.0' |
Affected Products
home assistant mcp serverhomeassistant-aiDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ha-mcp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ha-mcp to 7.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fmfg-9g7c-3vq7 is resolved across your whole dependency graph.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.
Frequently Asked Questions
Is GHSA-fmfg-9g7c-3vq7 in your dependencies?
Find it across PyPI, including transitive dependencies.