Loopback HTTP API publishes the action token and does not pin Host

Summary

The Token Meter server binds 127.0.0.1:8722 with no authentication. Mutation POSTs are gated by X-Token-Meter-Action, but that token is generated once at process start and then returned in ordinary GET JSON (/state, /session, /updates/status, /menubar).

GET handlers do not check Host or Origin. POST origin checks are skipped when the Origin header is absent:

origin = self.headers.get("Origin") or ""
if origin and (urlparse(origin).hostname or "") not in ("localhost", "127.0.0.1", "::1"):
    ...

Impact

Anyone who can speak to loopback can read session metadata, costs, project names, and the live action token, then call:

• POST /session/delete (move discovered .jsonl logs to Trash)
• POST /agent-access/toggle (add/remove the tokenmeter MCP entry in Codex/Claude)
• POST /capability/toggle and /capability/disable-unused (rewrite Claude/Codex plugin settings)
• POST /updates/install (fetch + reinstall)

That includes every local UID on a shared machine (curl 127.0.0.1:8722/state). DNS rebinding is also in play because there is no Host allowlist: GET is enough to exfiltrate the token and dashboard JSON. Classic HTML-form CSRF is mostly blocked by the JSON content-type requirement; local processes and rebinding pages are not.

Where

• token_meter/web/server.py (bind address)
• token_meter/app.py (_ACTION_TOKEN, software_update_status, do_GET / do_POST)
• menubar_software_update() also copies the token into /menubar

Suggested fix

1. Reject any request whose Host is not 127.0.0.1, localhost, or ::1 (with optional port).
2. Do not put the action token on unauthenticated GET JSON. Prefer a SameSite=Strict cookie, or a one-time bootstrap that is not readable cross-origin.
3. Require a loopback Origin on browser POSTs; do not treat a missing Origin as trusted.
4. Add Content-Security-Policy: frame-ancestors 'none' and X-Frame-Options: DENY so the dashboard cannot be clickjacked.

Happy to send a patch against a fork if useful.

Start by reading token_meter/web/server.py and the _ACTION_TOKEN, software_update_status, do_GET, do_POST, and menubar_software_update paths in token_meter/app.py. Trace how Host, Origin, GET JSON, and mutation requests are handled. Done means loopback host and browser-origin checks are enforced, GET responses no longer expose the action token, and the stated security headers protect the dashboard.