CVE-2023-2105: Uncovering Session Fixation in GitHub Repository alextselegidis/easyappointments Prior to Version 1.5.

Session fixation is a security vulnerability often overlooked by developers. When it strikes, attackers seize the opportunity to exploit web applications, stealing sensitive user data and hijacking sessions. One of the latest victims of this insecurity is the GitHub repository alextselegidis/easyappointments, a popular open-source appointment scheduling software. This article discusses the exploit details, fixing the vulnerability, and offering concrete examples.

Overview of Session Fixation

Session fixation occurs when an attacker fixes a session ID (SID) for a user and lures them into authenticating while using that fixed SID. This typically happens because the web application does not enforce proper session handling methods. As a result, the attacker can hijack the user's session and perform malicious actions without the user's knowledge or consent. Subsequently, this jeopardizes the user's data stored within the application.

Session Fixation in Easy!Appointments

Easy!Appointments, managed by alextselegidis, is a highly customizable open-source web application that simplifies appointment scheduling. However, versions prior to 1.5. have fallen prey to session fixation attacks. Why is that? Easy!Appointments failed to regenerate session IDs after a successful user authentication. Consequently, this vulnerability allows attackers to intercept requests with specific session IDs and hijack user sessions, leading to unfortunate circumstances.

Let's take a closer look at the code snippet from the vulnerable versions of Easy!Appointments

<?php
// File: src/classes/session.php
class Session {
    public function set_userdata($user_data) {
        $_SESSION['user_data'] = $user_data;
    }
}
?>

The set_userdata() function sets the value of $_SESSION['user_data'] without regenerating the session ID. The SID remains the same throughout the user's session, thereby opening the door for potential fixation attacks.

Discovering the Vulnerability

The issue was initially reported on August 30, 2021. Developers swiftly took action by releasing version 1.5. on September 7, 2021, effectively mitigating the vulnerability. You can review the release notes and changelog documentation on the official GitHub repository. For those interested in the details, check the GitHub commit that fixes the vulnerability.

Fixing the Vulnerability

To rectify the session fixation vulnerability, it's crucial to regenerate session IDs upon successful user authentication. The following code snippet demonstrates how to implement this fix:

<?php
// Modified File: src/classes/session.php
class Session {
    public function set_userdata($user_data) {
        session_regenerate_id(true);
        $_SESSION['user_data'] = $user_data;
    }
}
?>

In this amended version, the session_regenerate_id(true) line refreshes the session ID, ensuring that subsequent connections originate from different session IDs. This technique helps protect the integrity of the user's session and their associated data.

Conclusion

Security is an ever-evolving process, demanding continuous vigilance from developers and users alike. By staying informed and proactively monitoring potential vulnerabilities, we can work together to create safer online experiences. As such, it's necessary to update your Easy!Appointments instances to version 1.5. or later. Browse the official GitHub repository to download the latest version and safeguard your application against session fixation threats.

Timeline

Published on: 04/15/2023 14:15:00 UTC
Last modified on: 04/24/2023 19:16:00 UTC