How can a hacker exploit your cookies?

how to use cookies from a target
how to use cookies from a target

Last updated: July 7, 2023

Have you ever wondered how hackers manage to hijack user sessions? Have you ever heard of the sniffing techniques or exploitation of XSS flaws to recover a victim's cookies? But how do we actually use these cookies once they are in our possession? These topics are often discussed on the web, but the methods of using cookies are rarely explained.

In this article, we look at the exploitation of cookies. Let's assume you already have a cookie retrieved. How ? By a sniffer, perhaps? Or via a man-in-the-middle attack? Even simple access to a loved one's computer can be enough. However, it doesn't matter the method. Our objective here is precise: to exploit and use this cookie.

Info: Before we begin, it is important to emphasize that this article is for educational and informational purposes only. It aims to help readers understand how cookies can be exploited and used, to promote greater knowledge and better defense in computer security. Therefore, any information presented here must be used in compliance with applicable laws.

What is a cookie ?

What exactly is a cookie? In computing, a cookie is a small text file that is stored by a website on your hard drive via your browser. Its main role is to allow the site you are visiting to recognize you.

How do these cookies work? Imagine you return to a site several days after your last visit. The site then asks for your cookie. If it is still present on your hard drive, the site will read the information contained in the cookie and redirect you to your session without requiring new authentication.

So the main objective of a hacker is often to steal his victim's cookie. This would allow him to connect to her account without the need for authentication, thus facilitating his intrusion.

I have the victim's cookie but how can I use it?

You have the victim's cookie, but how can you use it? To do this, you will need the following tools:

  • Greasemonkey : This is an extension for Firefox that allows you to run JavaScript scripts on different web pages.
  • Cookie Injector : This is a script that allows you to inject a string of cookies into any web page.

Here is an example of use:

Once the two tools are installed, we will retrieve the cookie from a Facebook account on a Chrome browser and inject it on the Firefox browser. The same principle applies to the use of cookies from other websites.

Follow the steps below:

  • Open your Chrome browser and go to, then enter the login and password.
  • Next, type the following code in the address bar: “javascript:document.cookie”. This allows you to retrieve the cookie from the Facebook account.
  • Copy the displayed cookie.

  • Then open Facebook in the Firefox browser.
  • Type the following keys: ALT + C.
  • Paste the cookie into the text field.

Then relaunch Facebook. You can now access your session on the Firefox browser without having to enter a username or password.

To access a target's session, simply replace your cookie with that of the victim. »

NB: This article is intended to inform and educate users about possible online vulnerabilities and not to promote malicious activity.