Reading Time: 4 minutes

Session hijacking – aka TCP session hijacking, is a cyberattack that takes place during a user session. It happens when a cyberattacker intrudes an active session between the server of a site you’re visiting and your PC to steal some information.

In a hijacked session, the cyberattacker can easily monitor your activity. He can also kick you out of the session and take over if needed.

This can really take a toll on you if you’re using internet banking and your session gets hijacked in between. The attacker can acquire knowledge of your session ID through your cookie session, impersonate himself as you, and transfer money to his account.

While this type of hijacking can take place in any way, it’s more common to happen on browsing sessions of web apps.

Session Hijacking – How Does it Work?


(Image Credits:

There are multiple techniques that hackers use for carrying out session hijacking. These include session side-jacking, man-in-the-browser attacks, session fixation, predictable sessions token ID, session sniffing, and cross-site scripting.

Let’s check them out in detail:

1. Session side-jacking:

Session side-jacking is usually used in case of an unsecured Wi-Fi network. In this technique, a cyberattacker uses packet sniffing to monitor the network’s traffic and then intercepts the session cookies after the user has authenticated on its server.

In case the website uses TLS/SSL encryption for its login pages, the attackers can derive a session key from packet sniffing to impersonate the user and hijack their session.

2. Man-in-the-browser attack:

This type of attack is quite similar to man-in-the-middle attacks. The attacker has to first infect the user’s computer with the Trojan virus. As soon as the user has installed this malware on its computer, the Trojan malware waits for the user to visit any site.

This type of attack can easily modify the transaction details of any user and can create various other transactions behind the user’s back. Since all the transaction requests are made from the user’s system, websites cannot identify if they’re fake.

3. Session fixation:

This method tricks a user into authenticating an unauthenticated session ID. Once it’s authenticated, the cyberattacker can access the victim’s system.


(Image Credits:

4. Session sniffing:

Session sniffing is quite a basic method to hijack a user session. The cyberattacker uses Wireshark, the OWASP Zed proxy, or any other sniffer to capture a network’s traffic that contains the session ID between a client and a site.

Once he attains it, he can acquire unauthorized access using this token.


(Image Credits:

5. Cross-site scripting:

Cyberattackers use the vulnerabilities in a server or application for injecting client-side scripts into web pages. Due to this, every time a compromised page is loaded, the browser executes an arbitrary code.

If the session cookies aren’t set to HttpOnly, then using the injected scripts, attackers can access the session key, thereby getting the details required for session hijacking.

6. Predictable sessions token ID:

For generating session ID, various web servers use a predefined pattern or custom algorithm. If the predictability of a session token is high, then it’s quite easy to predict. If a hacker can analyze various patterns by capturing multiple session IDs, he can predict an accurate session ID.

What Do Cyberattackers Attain from Session Hijacking?

With an active hijacked session, attackers can do virtually everything the victim was privileged to do.

The attacks can range from being moderate to severe. The severe examples of session hijacking include stealing personally identifiable information (PII) for identity theft, transferring a huge amount of money from the victim’s account, and purchasing merchandise from online stores.

Examples of Session Hijacking

Using the compression ratio of TLS requests’ data leaks, attackers gain access to the login cookies of the user, which becomes the key to hijacking their sessions on various e-commerce websites and banks.

An attack like this came into the limelight in September 2012 when an organization of session hijackers named CRIME got involved in breaching a company’s website.

CRIME uses the brute force method to decrypt the HTTPS cookies to determine the authenticated users. The browser of the victim is then forced by the attack code to send specially crafted HTTPS requests to a website that’s being targeted and analyzes their length’s variation after being compressed, which helps in determining the worth of the session cookie of the victim.

This can only be possible since the TLS/SSL encryption uses DEFLATE, a compression algorithm that eliminates replicated strings.

The attack code cannot read the session cookie, but it can insert various strings and control the paths of all new requests. The values of session cookies can be quite extensive, but many algorithms have been developed for making the attacks efficient.

What Are the Risks and Consequences of Session Hijacking?

Successful session hijacking can allow an attacker to do anything the victim can do. This carries various significant risks in it. Let’s check out a few:

1. Identity theft:

Through session hijacking, attackers can gain access to personally identifiable information of users that can be used to steal the identity of these users.

2. Using SSO to gain access to additional systems:

By enabling the single sign-on method (SSO), cyberattackers can effortlessly access additional systems, thereby spreading the risk of session hijacking. This kind of risk is significant for companies that enable SSO for their employees.

3. Monetary theft:

Attackers can easily conduct various monetary transactions on behalf of the victim. This can involve online shopping through the saved payment details and transferring money to another account.

4. Data theft:

Cyberattackers can steal the company’s or personal data pre-saved in the web app and use it for their own benefit that can include causing harm to the company/victim.

How Can you Protect Against Session Hijacking?

Session hijacking, just like phishing, is one of the growing cybersecurity threats in the world. While there are quite a few ways to protect yourself from a cyberattack, here are some effective methods to be secure from session hijacking:

1. Alter the session key once authenticated:

To avoid this type of hijacking through the session fixation method, you must alter the session key after authentication at the time of login. This way, even if the attacker gets access to the actual session key, he won’t know the key to the entire session.

2. Use HTTPS only:

For completely secure page sessions, it’s quite important that you use HTTPS on every site and application. HTTPS makes sure that the SSL/TLS encryption is there throughout the session.

3. Use a VPN:

A virtual private network (VPN) is another way to prevent a session hijacking attack on your network. A VPN masks your original IP address and keeps you secure by creating an encrypted tunnel between yourself and the website. This way, no attacker will be able to intrude in your network.

There are various other benefits to getting a VPN. You should get a reliable VPN service and protect yourself from session hijacking and many other cyberattacks.

4. Add additional areas for identity information:

You can add another layer of protection to your network by introducing additional identity information beyond the session key. This includes checking the usual IP address of the user and the usage patterns.

5. Keep your systems up-to-date:

Enable automatic updates to keep your system up-to-date on all devices. You can also install reliable antivirus software so that you remain protected from all kinds of malware. This would also include the malware that attackers use for session hijacking.

You can also get an antivirus with a VPN so you can satisfy both your needs through one software.


Session hijacking is a significant threat that users are being victims of worldwide. However, there are multiple ways to protect yourself from these attacks. A few effective preventive measures are mentioned above.

These security measures require a deep understanding of the security protocols and encryption. If you’re missing that, it can lead to a significant data breach.

If you want to save your entire organization from session hijacking, you need to enlighten your employees with the best cybersecurity practices.