The Word Balloon WordPress plugin before 4.19.3 does not validate and escape some of its shortcode attributes before outputting them back in the page, which could allow users with a role as low as contributor to perform Stored Cross-Site Scripting attacks which could be used against high privilege users such as admins.
https://wpscan.com/vulnerability/dd5cc04a-042d-402a-ab7a-96aff3d57478