User enumeration is found in in PHPJabbers Class Scheduling System v1.0. This issue occurs during password recovery, where a difference in messages could allow an attacker to determine if the user is valid or not, enabling a brute force attack with valid users.
https://www.phpjabbers.com/class-scheduling-system
https://medium.com/%40bcksec/multiple-vulnerabilities-in-php-jabbers-scripts-25af4afcadd4