WordPress before 5.1.1 does not properly filter comment content leading to Remote Code Execution by unauthenticated users in a default configuration. This occurs because CSRF protection is mishandled and because Search Engine Optimization of A elements is performed incorrectly leading to XSS. The XSS results in administrative access which allows arbitrary changes to .php files. This is related to wp-admin/includes/ajax-actions.php and wp-includes/comment.php.