The Testimonial Slider WordPress plugin before 2.3.8 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example in multisite setup)
https://wpscan.com/vulnerability/5f35572a-4129-4fe0-a465-d25f4c3b4419/