A cross-site scripting (XSS) attack can cause arbitrary code (JavaScript) to run in a user's browser and can use an application as the vehicle for the attack. The XSS payload given in the "Custom logo link" executes whenever the user opens the Settings Page of the "Customize Login Image" Plugin.

A Cross-Site Scripting (XSS) attack can cause arbitrary code (JavaScript) to run in a user’s browser while the browser is connected to a trusted website. The attack targets your application's users and not the application itself while using your application as the attack's vehicle. The XSS payload executes whenever the user opens the login page of the WordPress application.