BigBlueButton is an open source web conferencing system. Starting with version 2.2 and prior to versions 2.3.9 and 2.4-beta-1, an attacker can circumvent access controls to obtain the content of public chat messages from different meetings on the server. The attacker must be a participant in a meeting on the server. BigBlueButton versions 2.3.9 and 2.4-beta-1 contain a patch for this issue. There are currently no known workarounds.