This indicates the detection of an attack attempt against a Cross-Site Scripting (XSS) vulnerability in WordPress Yoast SEO plugin.
The vulnerability is due to insufficient sanitization of user supplied data. A remote attacker maybe able to exploit this to execute arbitrary script code within the context of the application.
Yoast SEO plugin prior to 5.8.0
System Compromise : Remote attackers can execute arbitrary script code in the context of the affected site.
Upgrade to the latest version available from the website.