A Shadow of JWT Authentication - How Korean E-Commerce Giant Was Breached
At the end of 2025, a massive personal data breach involving South Korea’s largest e-commerce platform came to light. As of December 2025, the scale of the leak was reported to exceed 30 million. Behind this security incident lay the poor management of the company’s JWT (JSON Web Token) authentication system. A JWT signing key belonging to a former employee was not reset even after their departure, and the attacker was able to use this valid signing key to access customer data without restriction.
JWT-based authentication, which lies at the center of this incident, has become a standard in modern web and mobile applications. While it offers the convenience of stateless authentication, improper management can render it a single point of failure, potentially collapsing the entire authentication system.
This report introduces the concept of JWTs and their authentication mechanisms, then analyzes major vulnerabilities, and finally presents practical security strategies for prevention and mitigation.
