The Registration Forms – User Registration Forms, Invitation-Based Registrations, Front-end User Profile, Login Form & Content Restriction plugin for WordPress is vulnerable to Sensitive Information Exposure in all versions up to, and including, 3.8.3.9 through publicly exposed log files. This makes it possible for unauthenticated attackers to view potentially sensitive information about users contained in the exposed log files.
https://plugins.trac.wordpress.org/browser/pie-register/trunk/classes/base_variables.php#L68