The jQuery T(-) Countdown Widget WordPress plugin before 2.3.24 does not validate and escape some of its shortcode attributes before outputting them back in a page/post where the shortcode is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks.
https://wpscan.com/vulnerability/32324655-ff91-4a53-a2c5-ebe6678d4a9d