BigBlueButton is an open source web conferencing system. Starting in version 2.2 and up to versions 2.3.18 and 2.4.1, an attacker could send messages to a locked chat within a grace period of 5s after the lock setting was enacted. The attacker needs to be a participant in the meeting. Versions 2.3.18 and 2.4.1 contain a patch for this issue. There are currently no known workarounds.