WordPress Yuzo Related Posts plugin before 5.12.94 is vulnerable to cross-site scripting because it mistakenly expects that is_admin() verifies that the request comes from an admin user (it actually only verifies that the request is for an admin page). An unauthenticated attacker can consequently inject a payload into the plugin settings, such as the yuzo_related_post_css_and_style setting.
View the template here CVE-2019-11869.yaml
References:
https://www.wordfence.com/blog/2019/04/yuzo-related-posts-zero-day-vulnerability-exploited-in-the-wild