source: https://www.securityfocus.com/bid/24117/info

WÝYS is prone to a cross-site scripting vulnerability.

Exploiting this vulnerability may allow an attacker to perform cross-site scripting attacks on unsuspecting users in the context of the affected website. As a result, the attacker may be able to steal cookie-based authentication credentials and to launch other attacks.

WÝYS 1.0 is reported vulnerable; other versions may also be affected. 

http://www.example.com/index.php?Page=Sayfa&No="><script>alert(document.cookie)</script>