The WP Membership plugin 1.2.3 for WordPress allows remote authenticated users to gain administrator privileges via an iv_membership_update_user_settings action to wp-admin/admin-ajax.php.
https://wpvulndb.com/vulnerabilities/7998
https://euvd.enisa.europa.eu/vulnerability/EUVD-2015-4066
http://www.securityfocus.com/bid/74766
http://www.securityfocus.com/archive/1/535652/100/0/threaded
http://www.securityfocus.com/archive/1/535587/100/0/threaded
http://packetstormsecurity.com/files/132012/WordPress-WP-Membership-1.2.3-Privilege-Escalation.html