This research note is a follow-up to our April 3, 2020 report on the confidentiality of Zoom Meetings. We describe a security issue where users in the waiting room of a Zoom meeting could have spied on the meeting, even if they were not approved to join. Zoom fixed the issue after we reported it to them. On April 7, Zoom reported to us that they had implemented a server-side fix for the issue. In our testing, waiting room users did receive a video stream of the Zoom meeting prior to the fix.”]
Source: https://citizenlab.ca/2020/04/zooms-waiting-room-vulnerability/