Cracking JWTs: A Bug Bounty Hunting Guide [Part 6]

This article explains how JWT authentication can be bypassed through algorithm confusion by exploiting servers that trust the alg header without validation. It demonstrates a real-world proof-of-concept attack to impersonate administrators and delete user data, highlighting major security risks. #JWT #AlgorithmConfusion

Keypoints

JWTs specify the signing algorithm in the alg header, which can be exploited if blindly trusted.
Switching from RS256 to HS256 allows attackers to forge tokens using the server’s public key as a secret.
The attack involves extracting the server’s public key from the JWK endpoint and converting it into a symmetric key.
Adversaries can impersonate admin users and perform privileged actions, such as deleting user accounts.
Mitigation involves enforcing strict algorithm validation and not trusting client-supplied headers.