matrix-widget-api's host transport handled a message from ANY window on the
page as long as it carried the widget's id; its strictOriginCheck only
compares with the host's own origin and is off by default. The call's id is
the fixed 'call-embed', so any other frame (a room widget, a URL-preview
embed) could post fromWidget actions as the call. Reproduced locally: an
opaque-origin frame posting one io.lotus.hotkey keydown for the PTT key
turned a push-to-talk user's mic on ("● Live").
restrictWidgetMessages() swaps each ClientWidgetApi transport's listener
for one that requires ev.source === the widget iframe's window and
ev.origin === the widget's origin. Applied to the call and to room widgets
(so one widget can't impersonate another). Verified: the spoof no longer
opens the mic; PTT/deafen from inside the call, screenshare, speaking
indicator and room widgets (capability prompt, send, live events) unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA
