Joomla Extension - joomlaeventmanager.net - Cross-user event and venue takeover through forged form fields in Joomla Event Manager < 5.0.1 - A registered user with edit-own rights (the eventowner=1 setting or core.edit.own) can POST another user's record id together with their own id as created_by and take over that record.
Authorization Bypass Through User-Controlled Key The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.