The Securimage-WP-Fixed WordPress plugin is vulnerable to Reflected Cross-Site Scripting due to the use of $_SERVER['PHP_SELF'] in the ~/securimage-wp.php file which allows attackers to inject arbitrary web scripts, in versions up to and including 3.5.4.
https://www.wordfence.com/vulnerability-advisories/#CVE-2021-34640
https://plugins.trac.wordpress.org/browser/securimage-wp-fixed/trunk/securimage-wp.php#L628