The CSSable Countdown WordPress plugin through 1.5 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/ad714196-2590-4dc9-b5b9-50808e9e0d26/