The Slick Slider WordPress plugin before 0.5.3 does not sanitize and escape a shortcode attribute value before outputting it in an HTML attribute, allowing users with the Contributor role and above to perform Stored Cross-Site Scripting attacks that execute when a user views the affected post.
https://wpscan.com/vulnerability/8de9a050-45b5-4e51-9cd9-06f85999393a/