In a session prediction attack, the attacker attempts to guess an active session ID for a web application. This could be done by performing a brute force attack or deciphering, guessing, or reverse engineering the algorithm used to create session IDs.
Session identifiers (SIDs), sometimes called session keys or session tokens, are character strings used for user authentication in web applications. These strings are generated by the application after the user successfully logs in, presented to the user’s browser, and used across different web pages or functions of the application, usually via a session cookie. Since the web browser shares the session cookie with the application in every HTTP request, the application can use the session identifier to recognize a known user.
If it weren’t for session identifiers, we would have to log in to web applications much more frequently than we do. However, a session identifier has the same weakness as a password: it is only secure while it is secret. As soon as a malicious user knows your session ID, they can get access to your account and use it for further attacks and potential privilege escalation.
In general, malicious hackers will try to get access to session identifiers to impersonate users and gain access to their accounts/privileges. There are several specific attack techniques targeting sessions:
There are two primary types of session prediction attacks:
The first step of a session prediction attack is always gathering a (preferably) large number of current session IDs to create an initial dataset. The more IDs are available, the more certain the attacker can be about the structure and length of the session ID, increasing the chances of successful prediction.
Keep in mind that with the current developments in data mining, machine learning, deep learning, neural networks, and predictive models, attackers may well employ any or all of these techniques and methodologies to help them with deciphering existing session IDs and forecasting future session IDs.
Session prediction is not a specific type of vulnerability like SQL injection or cross-site scripting. The application may be vulnerable to session prediction attacks due to bad practices with session ID generation.
Session prediction vulnerabilities, like using predictable bases or easily decipherable algorithms, are similar to logical vulnerabilities and impossible to detect automatically. Because automatic vulnerability scanning is not able to detect such issues, you need manual penetration testing and security-focused code reviews to catch them.
There are several ways to prevent session fixation attacks through secure coding techniques:
Session prediction is a type of attack where the attacker attempts to guess an active session ID for a web application. This could be done by performing a brute force attack or deciphering/guessing the algorithm used to create session IDs.
If a session prediction attack is successful, the attacker can gain access to the user’s account in the web application. The consequences are similar to other session attacks, such as session hijacking. The potential damage depends entirely on the functionality of the web application and the privileges of the user, so accessing an administrator account for a major web application may expose large amounts of highly sensitive information.
Read more about related session hijacking attacks in our blog article.
The only way to prevent session prediction attacks is to follow best cybersecurity practices for developing web-based applications. Whenever possible, you should use dedicated, secure mechanisms to generate new session IDs. Most development frameworks include functions for generating non-predictable, safe, long session IDs. It’s always better to use ready session management mechanisms in frameworks instead of trying to generate IDs yourself.
Learn more about secure coding practices that help avoid attacks such as session prediction.