The WP Cerber Security plugin for WordPress is vulnerable to security protection bypass in versions up to, and including 9.0, that makes user enumeration possible. This is due to improper validation on the value supplied through the 'author' parameter found in the ~/cerber-load.php file. In vulnerable versions, the plugin only blocks requests if the value supplied is numeric, making it possible for attackers to supply additional non-numeric characters to bypass the protection. The non-numeric characters are stripped and the user requested is displayed. This can be used by unauthenticated attackers to gather information about users that can targeted in further attacks.