BigBlueButton is an open-source virtual classroom. A Denial of Service (DoS) vulnerability in versions prior to 3.0.13 allows any authenticated user to freeze or crash the entire server by abusing the polling feature's "Choices" response type. By submitting a malicious payload with a massive array in the "answerIds" field, the attacker can cause the current meeting — and potentially all meetings on the server — to become unresponsive. Version 3.0.13 contains a patch. No known workarounds are available.