The Popup Builder WordPress plugin before 4.2.3 does not prevent simple visitors from updating existing popups, and injecting raw JavaScript in them, which could lead to Stored XSS attacks.
https://wpscan.com/vulnerability/cdb3a8bd-4ee0-4ce0-9029-0490273bcfc8
https://wpscan.com/blog/stored-xss-fixed-in-popup-builder-4-2-3/