A Session Fixation issue was discovered in Bigtree before 4.2.24. admin.php accepts a user-provided PHP session ID instead of regenerating a new one after a user has logged in to the application. The Session Fixation could allow an attacker to hijack an admin session.
https://github.com/bigtreecms/BigTree-CMS/tree/4.2.24
https://github.com/bigtreecms/BigTree-CMS/commit/c69402c4764ed9a76301c57277aefe70141b6418
https://gist.github.com/zionspike/680eb504db7c86296fad0eff30c6317f