What Is Cookie Poisoning?

Cookie poisoning is a type of cyberattack where hackers tamper with website cookies to gain unauthorized access to sensitive data, user accounts, or control over web applications. Cookies store bits of information that websites use to recognize users, track sessions, and remember preferences. In a cookie poisoning attack, attackers manipulate these cookies to steal data, impersonate users, or even change transaction details.

This form of attack targets how websites handle session cookies, which manage user logins and track activity. If hackers alter these cookies, they can take over user sessions, posing a serious risk to web security.

How Does Cookie Poisoning Work?

In a cookie poisoning attack, the attacker changes the data stored in a cookie to trick the website into believing the hacker is a legitimate user. This allows them to access sensitive information or manipulate a user’s session, such as making unauthorized purchases or gaining admin-level access to accounts.

Client-side Cookie Poisoning

Client-side cookie poisoning happens when an attacker modifies cookies directly in the user’s browser. Many websites store critical data like session tokens in cookies. Hackers use browser tools or JavaScript to change the cookie values, letting them impersonate users or change sensitive data.

For instance, an attacker might inject malicious JavaScript into a website. This script could edit the cookie values to escalate user privileges or steal session data, enabling the hacker to take control of the account.

Man-in-the-middle Cookie Poisoning

Man-in-the-middle cookie poisoning occurs when hackers intercept data as it travels between a user’s browser and the website server. This type of attack is most common on unsecured Wi-Fi networks where traffic is not encrypted.

If an attacker can capture cookies during transmission, they can alter them and send them back to the server. This gives them unauthorized access to user sessions or sensitive information, like passwords or transaction details.

How Are Cookies Manipulated/Poisoned?

Cookies are manipulated or poisoned when hackers find ways to change the data they store. Some common ways cookies get manipulated include:

• Changing cookie values: Hackers can modify specific data in cookies, such as prices or user roles, to benefit themselves. For example, altering the price in a cookie during a checkout process to pay less for an item.
• Cross-Site Scripting (XSS): This attack method injects malicious code into a website, allowing the hacker to modify or steal cookies directly from the user’s browser.
• Intercepting data: When cookies are not transmitted securely over HTTPS, attackers can intercept them and change the contents during transmission.
• Poor cookie security: If cookies are not set with proper security settings, such as HTTPOnly or Secure flags, they are vulnerable to client-side tampering or being sent over unencrypted connections.

What Is an Example of Cookie Poisoning?

Let’s look at a practical cookie poisoning example to understand how attackers exploit this vulnerability.

Imagine you're shopping on an e-commerce website, and your shopping cart details, including the total price, are stored in a cookie. The cookie might look something like this:

In this case, the cookie stores the session ID and the total price of the items in your cart. If a hacker intercepts this cookie and changes the CartTotal from 500 to 50, they can effectively reduce the purchase price. When the manipulated cookie is sent to the website, the altered total will be processed, allowing the attacker to complete the transaction at a significantly lower cost.

This type of cookie manipulation is a classic example of how hackers can use cookie poisoning to commit fraud. Attacks like these can also be linked to phishing tactics, where users unknowingly provide attackers with access to their session data.

What Are The Causes of Cookie Poisoning?

Several factors can make a website vulnerable to cookie poisoning:

• Weak encryption: If cookies aren't encrypted, attackers can easily read and change their contents.
• Lack of secure flags: Cookies should be set with HTTPOnly and Secure flags to prevent them from being accessed by scripts or sent over unencrypted connections.
• No validation: When web applications fail to validate the data in cookies, hackers can inject malicious data and exploit vulnerabilities.
• Insecure communication: Sending cookies over HTTP instead of HTTPS leaves them open to interception, especially on public or unsecured networks. This risk can be mitigated with secure mobile device practices.

How to Detect Cookie Poisoning Vulnerabilities?

Detecting cookie poisoning vulnerabilities requires checking how cookies are handled by your website. Some ways to find these vulnerabilities include:

1. Perform vulnerability scans: Use automated tools to scan your website for cookie-related vulnerabilities like missing secure flags or unencrypted data.
2. Penetration testing: Simulate real-world attacks by conducting penetration tests on your web application. This can reveal weaknesses in how cookies are managed.
3. Check server logs: Look for unusual activity in your logs, such as suspicious session data or unexpected cookie changes, that might indicate tampering.
4. Inspect cookie settings: Make sure your cookies are set with HTTPOnly and Secure flags to prevent them from being tampered with by attackers. Learn more about protecting privacy in web environments.
5. Monitor traffic: Analyze your network traffic to see if cookies are being sent over unencrypted connections, which could expose them to interception.

How to Prevent Cookie Poisoning Attacks?

To prevent cookie poisoning attacks, start by ensuring your website uses HTTPS to encrypt all traffic, including cookies, so attackers can’t intercept them.

Set cookies with Secure and HTTPOnly flags to prevent them from being accessed by scripts or sent over unencrypted connections.

Always encrypt sensitive cookie data. Even if a cookie is stolen, the encryption will make the data unusable.

Regularly rotate session cookies and set them to expire quickly, reducing the chances of hijacking or misuse.

Ensure your web application properly validates all cookie inputs to block any harmful data.

Lastly, educate your users about avoiding public Wi-Fi for sensitive tasks or using a VPN for added security. Training employees is essential for a strong security posture.

Check out the video to learn more about cookie poisoning and prevention.

Protect Your Business from Cookie Poisoning Attacks with Keepnet’s Human Risk Management Platform

At Keepnet, we offer security awareness training to educate your employees on how to defend your business from cyber threats like cookie poisoning as well as phishing and social engineering attacks. Our security awareness training provides over 2,000 training modules that educate your employees on the latest phishing and social engineering tactics, reducing human error in cyber defenses.

The Phishing Simulator enables you to create realistic, customizable phishing simulations that help test and strengthen your team’s ability to recognize and respond to phishing threats. With global support and detailed reporting, it ensures that your defenses are continually improving.

See how you can use Evilginx2 with the Phishing Simulator below.

Ready to strengthen your security? Train your employees and try a free phishing simulation to assess and improve your organization’s resilience against phishing and other cyber threats.

This blog post was updated in October 2024.