The Serious Slider WordPress plugin before 1.2.7 does not validate and escape some of its shortcode attributes before outputting them back in a page/post where the shortcode is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks.
https://wpscan.com/vulnerability/7790af9d-621b-474c-b28c-c774e2a292bb/