The MDJM Event Management plugin's 'custom_fields_controller' function lacks proper capability checks, which should restrict access to sensitive operations. As a result, attackers can exploit this flaw by sending crafted requests to delete custom event fields without requiring authentication. This is primarily facilitated through the 'delete_custom_field' and 'id' parameters, allowing manipulation of data that should be protected by user permissions. Such vulnerabilities expose WordPress sites to potential data integrity issues, as unauthorized users can perform actions reserved for authenticated users with appropriate roles. The lack of capability checks is a common security oversight, often leading to significant operational disruptions if exploited. Addressing this issue involves reinforcing permission checks and updating the plugin to a secure version.

Administrators should immediately restrict access to the vulnerable functionality by employing web application firewalls or security plugins with customizable request rules. It's also critical to review user roles and capabilities regularly to ensure only authorized users have access to sensitive functions.