Update the WordPress Login/Signup Popup plugin to the latest available version (at least 2.3).
Chloe Chamberland (Wordfence) discovered and reported this Cross Site Request Forgery (CSRF) vulnerability in WordPress Login/Signup Popup Plugin. This could allow a malicious actor to force higher privileged users to execute unwanted actions under their current authentication. For example a password change which will then allow the malicious actor to login into the admin account. This vulnerability has been fixed in version 2.3.
Reflected CrossSite Scripting (XSS) vulnerability
Authenticated Stored CrossSite Scripting (XSS) vulnerability