The GS Logo Slider WordPress plugin before 3.3.8 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/e7dc0202-6be4-46fc-a451-fb3a25727b51