What is session hijacking and how do I prevent it?

Logging into websites or portals is part of many people’s daily routine. Each time you connect to one of these websites, a session is created. In the simplest possible way, a session is defined as the communication of two ongoing systems. This will remain active until the user ends the communication. This may be called a user-initiated session.

The start of a session is vital for any communication on the Internet. That being said, there is a constant threat of session hijacking looming. This article explains what session hijacking really is, how it happens, and what can be done to prevent it.

What is session hijacking?

Session hijacking is as the term suggests. A session user can be hijacked by an attacker and completely lose control of the session, where their personal data can easily be stolen. Once a user has started a session, for example by logging into a banking website, an attacker can hijack it.

In order to hijack a session, the attacker must have deep knowledge of the user’s session cookie. Although any session can be hijacked, it is most common in browser sessions on web applications.

How is a session hacked?

Attackers have a number of options to hijack a user’s session, depending on the attacker’s location and vector. Here are some of the ways a session can be hacked:

  • Cross-site scripting (XSS): Attackers exploit vulnerabilities in servers or applications to inject client-side Java scripts into users’ web pages, causing your browser to execute arbitrary code when it loads a compromised page. If the server does not set HTTPOnly in session cookies, injected scripts can access your session key, providing attackers with the information necessary for session hijacking.
  • Session side jacking: Using packet sniffing, an attacker can monitor network traffic and intercept user session cookies after authenticating them. If the website takes the low-cost route of using SSL/TLS encryption only for its login pages, the attacker can use the session key he derived from packet sniffing to hijack the user’s session. and impersonate it in order to perform actions in the web application. This can usually occur in the case of an unsecured Wi-Fi hotspot to access the network, monitor traffic, and configure their own hotspots to perform the attack.
  • Fixed session: Attackers provide a session key and spoof the user to access a vulnerable server.

The threat of session hijacking exists due to the stateless protocol. These protocols have limitations, which is why they are vulnerable to attacks.

Role of encryption

In order to protect a user’s session from hacking, organizations may incorporate certain encryptions. These encryptions are necessary to protect your consumers’ sessions and come in the form of certificates.

  • SSL: SSL stands for Secure Sockets Layer and, in short, it is the standard technology for securing an Internet connection and protecting all sensitive data that is sent between two systems, preventing criminals from reading and modifying any information transferred, including data potential personal.
  • TLS: TLS (Transport Layer Security) is just an updated and more secure version of SSL.

Example of session hijacking

A session attack takes advantage of data leaks in the compression ratio of TLS requests. This then gives them access to user login cookies which can be used to hijack the users session. One such incident occurred in September 2012, when a hijacker organization called CRIME hacked into an organization’s website.

CRIME ended up hijacking the session by decrypting the HTTPS cookies set by the website and authenticating itself as a user by brute force, siphoning off a massive amount of data.

How to prevent session hijacking

In order to protect yourself against hacking during a session, you need to strengthen the mechanisms of web applications. This can be done through communication and session management. Here are some ways to reduce the risk of session hijacking:

  • HTTPS: Using HTTPS ensures that there is SSL/TLS encryption in all session traffic. Attackers will not be able to intercept the plaintext session ID, even if the victim’s traffic was monitored. It is recommended to use HSTS (HTTP Strict Transport Security) to ensure full encryption.
  • HTTP only: Setting an HTTPOnly attribute prevents access to stored cookies from client-side scripts. This can prevent attackers from deploying XSS attacks that rely on injecting Java scripts into the browser.
  • System updates: Install reputable antivirus software that can easily detect viruses and protect you against all types of malware (including malware used by attackers to perform session hijacking). Keep your systems up to date by setting up automatic updates on all your devices.
  • Session management: In order to provide sufficient security, website operators can integrate web frameworks, instead of inventing their own session management systems.
  • Session key: It is advisable to regenerate session keys after their initial authentication. This makes the session ID extracted by attackers useless because the ID changes immediately after authentication.
  • Identity Verification: Perform additional user identity verification beyond the session key. This includes checking the user’s usual IP address or application usage patterns.
  • Public hotspot: Avoid using public WiFi to protect the integrity of your sessions and opt for secure wireless networks.
  • VPNs: Use a virtual private network (VPN) to stay safe from session hackers. A VPN hides your IP address and protects your session by creating a “private tunnel” through which all your online activities will be encrypted.
  • Phishing: Avoid falling for phishing attacks. Only click links in an email that you’ve verified was sent by a legitimate sender.


Session hijacking is a real threat and users are constantly at risk of being compromised. A website manager can mitigate these risks in several ways by implementing security protocols. These security protocols primarily involve deep encryption in entire web applications to close all entry points allowing attackers to hijack the user’s session.

With the vast increase in online data and more and more people using the web on a daily basis, it is essential for organizations to secure their websites. Failure to do so could result in heavy fines under global data privacy regulations.

Note: This blog post was written by a guest contributor in an effort to provide a greater variety of content for our readers. The views expressed in this guest author article are solely those of the contributor and do not necessarily reflect those of GlobalSign.

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