JWT Security in 2025: Are We Finally Free from Leaks?

If you’ve been working with authentication systems for a while, you already know the deal with JWTs. They’re everywhere. From API authentication to session management, JWTs have made life easier for developers. But here’s the million-dollar question — have we finally plugged all the security holes in JWTs?

The short answer? Not really.

Sure, we’ve come a long way from basic exploits like alg: none, but attackers have leveled up too. In 2025, JWT vulnerabilities are more sophisticated, and some of them are ridiculously sneaky. Let’s break them down one by one, understand how hackers bypass JWT protections, and, most importantly, see what we can do about it.

Modern JWT Attack Techniques That Still Work in 2025

Algorithm Confusion Attacks Are Still a Thing

A few years ago, JWTs had a glaring issue — if a server didn’t properly verify the alg parameter, an attacker could set alg: none, send a forged token, and get authenticated. That’s mostly fixed now.

But here’s the new trick: some systems still allow switching between RS256 and HS256, and that’s where the fun begins.

How the attack works:

• RS256 (RSA) uses a…