source: https://www.securityfocus.com/bid/25598/info
Toms Gastebuch is prone to multiple cross-site scripting vulnerabilities because it fails to properly sanitize user-supplied input.
An attacker may leverage these issues to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may allow the attacker to steal cookie-based authentication credentials and to launch other attacks.
These issues are related to the vulnerabilities discussed in BID 25507 (Toms Gästebuch Multiple Cross-Site Scripting Vulnerabilities) and may be a result of an incomplete fix for those issues.
http://www.example.com//admin/header.php?lang[adminseite]=XSS&lang[ueberschrift]=XSS&einst[metachar]=XSS