The WP User Manager – User Profile Builder & Membership plugin for WordPress is vulnerable to unauthorized access of data due to a missing capability check on the validate_user_meta_key() function in all versions up to, and including, 2.9.11. This makes it possible for authenticated attackers, with Subscriber-level access and above, to enumerate user meta keys.
https://plugins.trac.wordpress.org/changeset/3194404/wp-user-manager/trunk/includes/actions.php