The Anti-Spam by CleanTalk. Spam protection WordPress plugin before 6.79 does not properly sanitize content within a custom shortcode used in its email-encoding feature, allowing unauthenticated attackers to inject arbitrary web scripts into approved comments that will execute when any user (including administrators) views the post.
https://wpscan.com/vulnerability/0d4635b5-2d79-4337-a1ad-6b8d02cfd64b/