The MX Time Zone Clocks WordPress plugin before 3.4.1 does not escape the time_zone attribute of the mxmtzc_time_zone_clocks shortcode, allowing users with a role as low as Contributor to perform Stored Cross-Site Scripting attacks
https://wpscan.com/vulnerability/4e51dffa-027d-4f3d-a190-dcc5269f6435