The Collapse-O-Matic WordPress plugin before 1.8.3 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 admin.
https://wpscan.com/vulnerability/3b5c377c-3148-4373-996c-89851d5e39e5