exploiting-jwt-algorithm-confusion-attack

Overview of exploiting-jwt-algorithm-confusion-attack skill

What this skill does

The exploiting-jwt-algorithm-confusion-attack skill helps an agent test whether a JWT implementation trusts the token header too much, especially when alg can be changed from RS256 to HS256, set to none, or combined with key-header tricks like kid, jku, and x5u. It is most useful for Security Audit work where you need to confirm whether a server enforces a fixed signing algorithm instead of accepting attacker-controlled input.

Who should install it

Install the exploiting-jwt-algorithm-confusion-attack skill if you work on API security, JWT validation reviews, penetration testing with authorization, or defensive verification of auth middleware. It is a good fit when the goal is to prove or rule out token-forgery risk quickly, not to learn JWT theory from scratch.

Why it is different

This skill is built around a concrete attack path, supported by a reference file and a test script rather than only prose. That makes it more actionable than a generic prompt: users get a repeatable workflow for decoding a token, checking header trust, and testing confusion cases with less guesswork.

How to Use exploiting-jwt-algorithm-confusion-attack skill

Install and inspect the right files

Use the exploiting-jwt-algorithm-confusion-attack install path from the directory system, then open skills/exploiting-jwt-algorithm-confusion-attack/SKILL.md first. For implementation detail, read references/api-reference.md next, then scripts/agent.py to see the token parsing and forging helpers the skill expects. The repo does not include extra rules folders, so those three files are the practical starting set.

Give the skill a complete test brief

The exploiting-jwt-algorithm-confusion-attack usage flow works best when you provide: a sample JWT, the expected algorithm, where the token is used, and what you are allowed to test. Strong input looks like: “Review this RS256 access token for algorithm confusion in our staging API; check whether alg downgrade, none, or kid/jku handling could bypass verification.” Weak input like “break this JWT” leaves the model guessing the target and constraints.

Follow a short analysis workflow

Start by decoding the header and payload, then identify the expected signing model from the application or API docs. Test only the smallest relevant branch first: algorithm downgrade, none, or header injection. If the first result is inconclusive, ask for a second pass focused on library behavior, key handling, or server-side verification settings rather than expanding the attack surface all at once.

Read the repo in this order

For the fastest exploiting-jwt-algorithm-confusion-attack guide experience, read SKILL.md for triggers and prerequisites, references/api-reference.md for the attack flow and example structures, and scripts/agent.py for how the skill constructs or inspects JWTs. That order helps you understand both intent and execution before adapting it to your own environment.

exploiting-jwt-algorithm-confusion-attack skill FAQ

Is this only for offensive testing?

No. The exploiting-jwt-algorithm-confusion-attack skill is best treated as a validation tool for Security Audit, bug hunting with authorization, or defensive red-team simulation. If your goal is to harden an API, it helps you identify whether the implementation is accepting unsafe JWT headers or misusing public keys.

Do I need an advanced prompt to use it?

No, but you do need a precise target. Ordinary prompts often miss whether the server uses RS256, HS256, or none, which is the core decision point here. A better prompt includes the token type, environment, and what evidence you already have about JWT verification.

When should I not use this skill?

Do not use it when you only need generic JWT explanation, when the app uses opaque sessions instead of JWTs, or when you lack explicit authorization to test authentication bypass behavior. It is also a poor fit if the task is mostly code review of unrelated auth logic without an actual JWT verification path.

Is it beginner-friendly?

It is beginner-usable if you can provide a token and follow a guided workflow, but it is not a teaching-first skill. The main risk for beginners is assuming any JWT is vulnerable; in practice, the result depends on how the server validates algorithm and key material.

How to Improve exploiting-jwt-algorithm-confusion-attack

Provide the strongest target context

To improve exploiting-jwt-algorithm-confusion-attack results, include the issuer, expected algorithm, sample claims, where the token is stored or sent, and any verification library you know about. If you know the app uses RS256, say so explicitly; that changes the most likely confusion path and reduces wasted analysis.

Share the exact failure mode you want checked

Ask for one primary test at a time: alg:none, RS256-to-HS256 downgrade, public-key-as-HMAC-secret confusion, or kid/jku/x5u header abuse. Mixing all four in one request usually leads to shallow output; separating them produces cleaner, more useful checks and clearer pass/fail reasoning.

Refine after the first result

If the first pass says “likely safe,” ask what evidence would falsify that conclusion, such as library defaults, key lookup logic, or header validation gaps. If it says “vulnerable,” ask for a minimal proof path and a defensive fix checklist so the output is useful for reporting, retesting, and remediation.

Ask for validation-friendly output

For better Security Audit use, request a concise outcome format: observed token structure, suspected weakness, how to verify it safely, and what server-side control should block it. That keeps the exploiting-jwt-algorithm-confusion-attack skill focused on evidence, not speculation, and makes the result easier to hand to engineering teams.