The uListing plugin for WordPress is vulnerable to authorization bypass via Ajax due to missing capability checks, missing input validation, and a missing security nonce in the stm_update_email_data AJAX action in versions up to, and including, 1.6.6. This makes it possible for unauthenticated attackers to change any WordPress option in the database.
https://blog.nintechnet.com/wordpress-ulisting-plugin-fixed-multiple-critical-vulnerabilities/