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Advanced Exploitation using XSS-SHELL

Before getting into XSS Shell, let us recollect few basics of XSS (Cross Site Scripting). XSS is one of the most common vulnerability that exists in many of the web applications today. XSS is a technique through which an attacker tries to compromise the web application by executing a malicious script. The attacker does this by breaking the Same-Origin policy of the web application. Same–Origin policy defines that the script which is coming from the foreign site or the script that doesn’t belongs to the same domain (i.e document.domain) should not be processed by the application.

Once if an attacker finds XSS in a web application, he can perform different kinds of attacks.
– Stealing Credentials
– Stealing Session tokens
– Defacing the Website
– Causing DOS
– Installing Key loggers and many more….

Cross-Site-Scripting exists in three different forms:
– Reflected
– Stored
– DOM Based

Reflected XSS:
This kind of vulnerability exists in the application that uses dynamic pages to display the content to the user. Normally these applications take the message into a parameter and renders back to the users.

For Example, consider the URL: http://www.[sample].com/error.html?value=learn+hacking

This shows the message learn hacking in the response of the application. Which means the application is extracting the message from the URL, processing it and displaying it to the user. So the URL processes user supplied data and inserts it into the server’s response. If there is no proper sanitization then the application is vulnerable to Reflected XSS.

The URL can be crafted as: http://www.[sample].com/error.html?value=<script>alert(1)</script>

When you click on the above URL it executes the script and pops up an alert box.

Stored XSS:
This type of vulnerability exist in applications which takes input from the user, store it and later displays to other users. For example, consider Facebook application which allows commenting on any picture or status update and then displays to all other users. If the application doesn’t sanitize the input properly then an attacker can write a script in the comment area, so that the users who visits or views particular page or post will be effected.

So Stored XSS consists of two things to do. Initially the attacker enters the malicious script into the application. Secondly the user visits the crafted page and the script is executed in the back-end without the knowledge of the user.

DOM Based XSS:
DOM stands for Document Object Model. It is quite different from the other two attacks described earlier. In DOM Based XSS when the user click on the crafted URL, server response doesn’t consist of attacker’s script. Instead the browser executes the malicious script while processing the response. This is because the Document Object Model of the browser has a capability to determine the URL used to load the current page. Script issued by the application may extract the data from the URL and process it. Then it uploads the content of the page dynamically depending upon the script executed through the URL.

XSS Shell

XSS Shell is a powerful tool developed in ASP .NET which runs as a XSS backdoor between the attacker and the victim. With XSS, attacker has only one shot to execute any kind of attack on victim. Once the victim navigates from the malicious page the attacker’s interaction or the communication with the victim ends, whereas using XSS Shell help the attacker to open an interactive channel with the victim and communicate with him by sending its commands. Here, even if the victim navigates from the vulnerable/malicious page the attacker can continue his communication as the XSS Shell re-generates the page.

The interactive shell or the communication channel which was established by the attacker with the victim is called “XSS Tunnel”. XSS Tunnel is used for tunneling the HTTP Traffic between two machines opened by XSS. Technically it is developed using AJAX and that can send requests and receive responds and has an ability to talk cross-domain.

Attack Process:
1. Setup XSS Shell Server.
2. Configure XSS Tunnel to use XSS Shell Server.
3. Inject malicious script into a vulnerable Website.
4. Launch XSS Tunnel and wait for victim.
5. Configure the browser or tool to use XSS Tunnel.
6. When victim visits the vulnerable page, start using XSS Tunnel.

How XSS Shell works:

xss shell process 1

As shown in the figure, initially attacker establishes a connection with the XSS Shell and injects malicious script into the web Application using Stored or Reflected XSS. Once the victim clicks or visits the vulnerable application with the malicious script a request will be sent to the XSS Shell Server. On the basis of the request server establishes a channel to interact with the victim.

xss shell process 2

Once a channel has been created between the victim and XSS Shell Server, attacker can control the communication through XSS Shell Admin Interface. XSS Shell Admin Interface is nothing but a GUI environment which provides definite set of commands which the attacker can execute to perform certain actions.

On executing a command, necessary function or the script will be called at XSS Shell Server level and it is sent to the victim. The script will be processed and executed at victim browser and it sends corresponding results to the XSS Shell Server. XSS Shell Server stores the results in MS-Access database which is normally used by it to store the data. Attacker can extract the results from the database and look at it whenever he wants.

Some of the commands that XSS Interface provides are:
– Get Cookie
– Get Current Page
– Get Clipboard
– Get Key-logger data
– Crash browser

One more advantage of using XSS Shell is, it is an Open Source and quite easy to implement new commands.

Requirements:
– An IIS Server where you can host .asp files.
– Microsoft Access database (.mdb)
– A Website which is vulnerable to XSS
– A vulnerable site to perform attack

Setting up the environment:
– Download the XSSShell from: http://labs.portcullis.co.uk/download/xssshell-xsstunnell.zip
– Configure IIS to host the site
– Installation
– Configure XSS Shell

Configuring IIS:
In-order to configure IIS in windows 7 or above, follow the steps given below:

1. Click on Start Menu and goto Control Panel.
2. Click Programs and then click on Turn windows features on or off.
3. A new Windows Features dialog box will appear. Expand Internet Information Services.
4. Select default features that has to be installed with IIS.
5. You can expand the additional categories and install any additional features if required.
6. It is recommended to install additional features if you want to use IIS for evaluation purpose.

Now IIS has been configured in the machine and can be accessed using http://localhost/

IIS 7 default page

Installation:
XSS Shell uses ASP .NET and MS-Access database. So just make sure that you have installed .NET framework and MS-Access db on your machine.

Configuring XSS Shell Admin Interface:
– After downloading the XSSShell.zip file, extract the file and you can see two folders – XSSshell & XSSTunnel.
XSSshell is admin interface and you need to configure it in your machine. Copy XSSshell folder to your web server.

xss shell folder

– You can see a sub-folder named db in the XSSShell folder as shown in the above image. Copy that to a secure place because XSSshell stores complete data in that db, whatever it is either victim’s session cookies or any other attacked data that belongs to victim.
– After moving the db folder to a secure place, configure the path in db.asp file under XSSshell/admin folder. So that the interface can know where the db is and interact with it.

xssshell source 1

– Edit the path to the location such that it should point to the place where db folder is present in your machine.xssshell source 2– The above image, shows default password to access shell.mdb file. You can edit to whatever you want.
– Now you can access admin interface by using the localhost url or the domain name that you have given. Ex: http://localhost/xssshell (or) http://yourhostname.com/xssshell
– By default it uses port 80, but if you change the port number while configure the domain you need to access the site by embedding the port number.

Configuring XSS Shell:
– Open xssshell.asp from XSSshell folder.
– Configure the server path. i.e to the place where XSSshell folder is located.

xssshell source 3

– Above figure shows the configuration of server path in xssshell.asp file. Edit he parameter SERVER to the place to the location of XSSshell folder in your machine.
– Now access your admin interface from the browser, which would contain three sections.

xss shell admin interface

Commands:
As mentioned earlier XSSshell has pre-defined commands which make attacker’s life easy to perform any attack on the victim. Commands section contains all the commands supported by the shell. As it is a open source you can edit it and add your own functionalities there.

Victims:
Victims section shows the list of victims.

Logs:
Logs show the list of actions performed on the victims.

XSS Tunnel:

XSS Tunnel is just like a proxy tool which runs on attacker machine and captures traffic through xss channel on XSSshell server. In-order to do this XSS Tunnel should be able to understand where XSSshell server is running. We can configure the XSSshell information (i.e where it is running) in XSS Tunnel from Options tab. Enter the server address and password. Then just to make sure it is working fine click on Test Server. You get a success message if the configuration is proper.

xss tunnel - connection success

Once done with configuration, click on Start XSS Tunnel on the top of the window.  Then you can see all the actions performed by the victim from XSS Tunnel’s Dashboard. The below image shows all the pages visited by the victim and actions performed.

xss tunnel - traffic capture

Conclusion:

XSSshell is an interface or a tool which opens a gateway to the attacker through which he can perform various attacks on the victim without losing the connection once established.

References:

http://labs.portcullis.co.uk/tools/xss-shell/
http://www.slideshare.net/clubhack/xss-shell-by-vandan-joshi

 

Posted by on January 29, 2014 in web application hacking

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