The Countdown Timer for WordPress Block Editor WordPress plugin through 1.0.5 does not validate and escape some of its block options before outputting them back in a page/post where the block is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks.
https://wpscan.com/vulnerability/b153fb5e-7df2-491b-b61b-6f90314c7b04/