Update the WordPress Login/Signup Popup plugin to the latest available version (at least 2.2).
WPScanTeam discovered and reported this Cross Site Scripting (XSS) vulnerability in WordPress Login/Signup Popup Plugin. This could allow a malicious actor to inject malicious scripts, such as redirects, advertisements, and other HTML payloads into your website which will be executed when guests visit your site. This vulnerability has been fixed in version 2.2.
CrossSite Request Forgery (CSRF) vulnerability leading to Arbitrary Options Update
Authenticated Stored CrossSite Scripting (XSS) vulnerability