PortSwigger “JWT authentication bypass via algorithm confusion” Lab Çözüm & Rehber

📰 Medium · Cybersecurity

Learn how to bypass JWT authentication via algorithm confusion attacks and understand the vulnerability in RS256 and HS256 algorithms

intermediate Published 19 Apr 2026

Action Steps

Identify the difference between RS256 (asymmetric) and HS256 (symmetric) algorithms
Understand how algorithm confusion attacks work by exploiting the trust in the 'alg' field in the header
Use tools like Burp Suite or JWT toolkit to modify the 'alg' field and test the vulnerability
Implement proper validation and verification of JWT tokens to prevent algorithm confusion attacks
Use secure practices like using a secure secret key and keeping it confidential

Who Needs to Know This

Security teams and developers can benefit from understanding this vulnerability to protect their applications from algorithm confusion attacks

Key Insight

💡 Algorithm confusion attacks exploit the trust in the 'alg' field in the header, allowing attackers to bypass JWT authentication without knowing the secret key