The Hacker's Guide to JWT Security

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Patrycja Wegrzynowicz is a software visionary and expert specialized in automated software engineering, security, and Java technologies. She is the founder and CTO of Yon Labs, a start-up focused on automated detection and refactoring of software defects, including security vulnerabilities, performance, and concurrency anti-patterns, and database issues.

Patrycja is a regular speaker at major academic as well as industrial conferences, including CodeOne, JavaOne, Devoxx, JavaZone, and others. She was awarded Oracle Groundbreaker Ambassador title in 2020 and in 2021. She was also named as one of the Top 10 Women in Tech in Poland in 2016 by Girls in Tech.

Patrycja’s interests focus on patterns and anti-patterns in software along with automated software engineering, particularly static and dynamic analysis techniques to support program verification, comprehension, and optimization.


JSON Web Token (JWT) is an open standard for creating tokens that assert some number of claims like a logged in user and his/her roles. JWT is widely used in modern applications as a stateless authentication mechanism. Therefore, it is important to understand JWT security risks, especially when broken authentication is among the most prominent security vulnerabilities according to the OWASP Top 10 list.

This talk guides you through various security risks of JWT, including confidentiality problems, vulnerabilities in algorithms and libraries, token cracking, token sidejacking, and more. In live demos, you’ll learn how to hijack a user account exploiting common security vulnerabilities on the client-side, on the server-side, and in transport. You’ll also find out about common mistakes and vulnerabilities along with the best practices related to the implementation of JWT authentication and the usage of available JWT libraries.