Session fixation is a cyberattack that exploits vulnerabilities in web browsers' session management systems, allowing attackers to hijack users' sessions by tricking them into using a session ID the attacker already knows. This attack can compromise web applications' security, potentially leading to data breaches and unauthorized access to user accounts, as exemplified by the CVS data breach in 2021. Unlike session hijacking, where attackers intercept an existing session ID, session fixation involves pre-setting a session ID for a user to authenticate unknowingly. Preventing session fixation requires robust security measures, such as regenerating session IDs upon login, using secure session identifiers, implementing HTTPS, and enforcing session expiration. Developers can mitigate these risks through secure session management practices or by using platforms like Descope, which offer seamless and secure solutions for managing web application sessions.