source: https://www.securityfocus.com/bid/21792/info

PHP icalendar is prone to multiple cross-site scripting vulnerabilities because the application fails to properly sanitize user-supplied input.

An attacker may leverage these issues to have arbitrary script code execute in the browser of an unsuspecting user. This may help the attacker steal cookie-based authentication credentials and launch other attacks.

http://www.example.com/phpicalendar/week.php?cal=all_calendars_combined971 &getdate=20061225"><script>alert()</script>