Update the WordPress Custom Field Suite plugin to the latest available version (at least 2.6.3).
Taihei Shimamine discovered and reported this Cross Site Scripting (XSS) vulnerability in WordPress Custom Field Suite Plugin. This could allow a malicious actor to inject malicious scripts, such as redirects, advertisements, and other HTML payloads into your website which will be executed when guests visit your site. This vulnerability has been fixed in version 2.6.3.