Greenlight is an end-user interface for BigBlueButton servers. Versions prior to 2.13.0 have an open redirect vulnerability in the Login page due to unchecked the value of the `return_to` cookie. Versions 2.13.0 contains a patch for the issue.
https://huntr.com/bounties/ba5834bd-1f04-4936-8e93-2442d45403bahttps://
https://github.com/bigbluebutton/greenlight/commit/20fe1ee71b5703fcc4ed698a959ad224fed19623