3 Ways JWTs Get Forged, and the One Rule That Stops Them All

This story was originally published on HackerNoon at: https://hackernoon.com/3-ways-jwts-get-forged-and-the-one-rule-that-stops-them-all.
A practical walkthrough of three JWT forgery attacks involving unsigned tokens, weak secrets, and algorithm confusion.
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I walk through the three JWT attacks I actually test for: changing the algorithm to none, cracking weak HMAC secrets offline, and confusing an RS256 verifier into accepting an HS256 token signed with the public key. All three exploit weak assumptions in how the server verifies the token.