What is Session Hijacking and how to prevent it?

Posted at October 14, 2016 at 4:00 pm by Jithin

What is Session Hijacking?

The session hijacking is a type of web attack. It works based on the principle of computer sessions. The attack takes advantage of the active sessions. To know this in detail, we need to know what is a session. Let’s see what is a session and how the session works first.

 

What is a session?

The session refers to certain time period that communication of two computer systems or two parts of a single system takes place. When one logins to a password protected system, the session is used. The session will be valid up to the end of the communication. In some cases, such as in the above described case, the session is user-initiated. There is technology initiated sessions also. Various email clients use the sessions and these are examples for the sessions initiated by the technology. However, many of the active sessions will be hidden from the users. They will not know when a session starts and ends. The session is an important factor in the Internet communications.

Coming to the session hijacking, as we’ve seen earlier, the attacker uses the active session for implementing the attack. For most Internet communications, authentication will be needed. Authentication can be done in different methods. The most used method is the user is asked to enter a predefined username and password by the website. When the user enters this credentials, the system will check the same with the stored details. If the entered details match with the stored details, the system grants access to the particular user to the particular database or part of the website.

This type of authentication is done at the start of the communication and when the authentication completed successfully, then the session starts and remains active up to the end of the communication. The session hijacking attack takes place in such a fashion that when a session is active the attacker intrudes at the same time and takes advantage of the active session. This intrusion may or may not be detectable. Every session will be having a session id. This session id will be often stored in cookies or URLs. This attack is also called “Cookie Hijacking”. We can recognize a session hijacking attack by the behavior of the website that uses the current session. If the website does not respond in the expected way to the user inputs or if it completely stops working for unknown reason, it can be the result of a session hijacking attack.

 

How Does Session Hijacking Works?

As we know, the http communication uses many TCP connections and so that the server needs a method to recognize every user’s connections. The most used method is the authentication process and then the server sends a token to the client browser. This token is composed of a set of variable width and it could be used in different ways, like in the URL, in the header of http requisition as a cookie, in other part of the header of the http request or in the body of the http requisition. The attack compromises the session token by stealing or predicting a valid session token to gain unauthorized access to the web server. This compromising of session token can occurr in different ways. We are now going to see the two ways as session sniffing and cross-site script attack.

 

Session Sniffing

As we’ve seen earlier, there is a string called tokens. This is the session id of a valid session. The first step by the attacker is getting this session id. The attacker uses a sniffer to get the session id. When the session id is captured, the attacker uses this session id to gain unauthorized access to the web server.

 

The Cross-Site Script Attack

The cross-site script attack is a way to get the session id with the helping of running malicious code or script from the client side. In this attack, the attacker executes malicious scripts, also known as malicious payloads into a legitimate website or web application. By using this attack, the attacker does not target a victim directly, but the attacker could exploit a vulnerability in a website that the victim would visit and use the website to deliver malicious script to the victim’s browser.

 

 How to prevent the Session Hijacking?

As we’ve seen earlier, the method often used to steal session id is by installing a malicious code on the client website and then the cookie is stealing. The best way to prevent session hijacking is enabling the protection from the client side. It is recommended that taking preventive measures for the session hijacking on the client side. The users should have efficient antivirus, anti-malware software, and should keep the software up to date.

There is a technique that uses engines which fingerprints all requests of a session. In addition to tracking the IP address and SSL session id, the engines also track the http headers. Each change in the header adds penalty points to the session and the session gets terminated as soon as the points exceeds a certain limit. This limit can be configured. This is effective because when intrusion occurs, it will have a different http header order.

These are the recommended preventive measures to be taken from both the client and server sides in order to prevent the session hijacking attack.

 

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