The Testimonial Slider Shortcode WordPress plugin before 1.1.9 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/b8390b4a-b43f-4bf6-a61b-dfcbc7b2e7a0