GHSA-9c5c-5j4h-8q2c

BookStack prior to version 21.11.3 is vulnerable to Improper Access Control. A logged-in user with no privileges OR guest user (if public access enabled) can access the /search/users/select AJAX endpoint meant for admins to manage audit logs, to dump all usernames existing in the Bookstack database. This can also be used to harvest email belonging to a user because BookStack also uses the code where(`email`, `like`, `%` . $search . `%`) to search for users based on email.