WordPress All-in-One Event Calendar plugin’s /wp-content/plugins/all-in-one-event-calendar/app/view/save_successful.php “msg” parameter is prone to a cross-site scripting vulnerability. It fails to properly clean up user-supplied input. An attacker may execute arbitrary script code in the browser of an user in the context of the affected site. In this way the attacker can steal cookie-based authentication credentials. Other attacks are also possible.
Update the plugin.