The Balbooa Gridbox extension version 2.4.0 and previous versions for Joomla! is vulnerable to cross-site scripting, caused by improper validation of user-supplied input. A remote attacker could exploit this vulnerability via a crafted URL to execute script in a victim's Web browser within the security context of the hosting Web site, once the URL is clicked. An attacker could use this vulnerability to steal the victim's cookie-based authentication credentials.