WordPress Stop Spammers plugin before 2021.9 contains a reflected cross-site scripting vulnerability. It does not escape user input when blocking requests (such as matching a spam word), thus outputting it in an attribute after sanitizing it to remove HTML tags.
View the template here CVE-2021-24245.yaml
References:
https://packetstormsecurity.com/files/162623/WordPress-Stop-Spammers-2021.8-Cross-Site-Scripting.html