Rocket.Chat is an open-source, secure, fully customizable communications platform. Prior to 7.10.14, 8.0.8, 8.1.7, 8.2.7, 8.3.7, 8.4.5, 8.5.2, and 8.6.1, the stream-notify-user stream in the WebSocket protocol allows an authenticated user to write arbitrary notification bodies because the sender is not checked, and the client-side UI can create an ephemeral fake message in another user's currently open chat. This issue is fixed in versions 7.10.14, 8.0.8, 8.1.7, 8.2.7, 8.3.7, 8.4.5, 8.5.2, and 8.6.1.