BigBlueButton is an open-source virtual classroom designed to help teachers teach and learners learn. An attacker with a valid join link to a meeting can trick BigBlueButton into generating a signed join link with additional parameters. One of those parameters may be "role=moderator", allowing an attacker to join a meeting as moderator using a join link that was originally created for viewer access. This vulnerability has been patched in version(s) 2.6.18, 2.7.8 and 3.0.0-alpha.7.