An issue was discovered in eGroupWare 17.1.20190111. A cross-site scripting Reflected (XSS) vulnerability exists in calendar/freebusy.php, which allows unauthenticated remote attackers to inject arbitrary web script or HTML into the "user" HTTP/GET parameter, which reflects its input without sanitization.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.