Closes#366 (reported by JohnBaumb).
Socket.IO was initialized with `cors_allowed_origins='*'`, accepting
WebSocket connections from any origin. A malicious site could open a
WS to a user's local SoulSync instance and exfiltrate live progress /
toast / activity events.
This commit:
- Defaults to engineio's same-origin behavior (`cors_allowed_origins=None`),
which automatically honors X-Forwarded-Host so reverse proxies that
send that header (Caddy / Traefik by default, properly-configured
Nginx) work transparently.
- Adds a `security.cors_origins` config setting + Settings → Security
textarea where users behind unusual proxies / Electron wrappers /
cross-origin integrations can whitelist their origin. Accepts comma
or newline separated values; `*` on its own line opts back into the
legacy wildcard with a startup-warning log.
- Logs a clear warning the first time engineio rejects each unique
origin, naming the rejected Origin and request Host and pointing
users to the settings field. Without this, engineio silently 403s
the upgrade and the user just sees a half-broken UI with no clue
why. Threadsafe dedup so a hostile origin can't spam logs.
Logic lives in `core/socketio_cors.py` (resolver, rejection
predictor, dedup logger class, startup-status emitter) — pure
functions, no Flask dependency. `web_server.py` adds 23 lines of
wiring and imports.
Important catch during review: my first pass used `cors_allowed_origins=[]`
as the "secure default." Reading engineio's source revealed `[]` actually
means "DISABLE CORS HANDLING" (engineio/server.py:202: `if cors_allowed_origins != []:`)
— identical security to `'*'`. Fixed to use `None` (engineio's actual
same-origin sentinel) and pinned with a regression test that asserts
the resolver never returns `[]` for any input shape.
Tests:
- tests/test_socketio_cors.py — 45 unit tests covering 19 resolver shape
cases (None, empty, whitespace, comma, newline, garbage types, lists),
the `[]`-must-never-be-returned security regression, 12 rejection
prediction cases, X-Forwarded-Host handling, dedup logger behavior,
threadsafe race (8 threads × 50 hammers → exactly 1 warning), and
startup-status emitter outputs.
Frontend:
- Settings → Security gains an "Allowed WebSocket Origins" textarea
with help text explaining same-origin default + when to add a domain
+ the `*` opt-out.
- helper.js — new '2.4.1' WHATS_NEW block (hidden until version bump)
with a chill-voice entry describing the change.
Conftest.py left at `'*'` — test environment, no security concern.
598 tests pass.
