Offensive Jwt
JWT attack methodology for penetration testers.
Install
npx skills add SnailSploit/Claude-Red --skill offensive-jwt -g -a claude-code -y- Repository
- SnailSploit/Claude-Red10.2k
- Category
- Testing
- Updated
- 23d ago
- License
- MIT
- Context cost
- Mediumabout 2,545 tokens
- Runs scripts
- No, instructions only
What it does
JWT attack methodology for penetration testers. Covers algorithm confusion (alg:none, RS256→HS256), weak HMAC secret brute force, kid parameter injection (SQLi, path traversal), jku/x5u/jwk header injection, JWKS cache poisoning, JWS/JWE confusion, timing attacks, and mobile JWT storage extraction. Use when testing JWT-based authentication, hunting auth bypass via token manipulation, or evaluating JWT implementation security in web or mobile apps.
Overview
Comprehensive JWT attack checklist for offensive security engagements. Follow steps in order; apply each technique to the current target context and track which items have been completed.
Quick Reference: Misconfigurations to Check
- Algorithm set to
none, signature verification bypassed entirely - Algorithm switching between
RSAandHMAC(confusion attack) - Weak or guessable HMAC secret (brute-forceable)
kid,jku,jwk,x5uheader parameters accepted without validation- Expired or tampered tokens accepted by server
- Sensitive data stored unencrypted in payload
Useful tool: JWT Tool
Mechanisms
JWTs (RFC 7519) consist of three Base64URL-encoded parts: header.payload.signature.
Signing algorithms:
| Algorithm | Type | Notes |
|---|---|---|
| HS256/384/512 | Symmetric HMAC | Shared secret; confusion target |
| RS256/384/512 | Asymmetric RSA | Public key can be misused as HMAC secret |
| ES256/384/512 | Asymmetric ECDSA | |
| PS256/384/512 | RSASSA-PSS | |
| EdDSA (Ed25519/Ed448) | Asymmetric | |
| none | Unsigned | Critically insecure |
Additional pitfalls:
- JWS/JWE confusion: server accepts encrypted token (JWE) where signed (JWS) is expected, or fails open on unexpected
typ/cty - JWKS retrieval: SSRF via
jku/x5u, insecure TLS, poisoned key caching,kidcollisions - Token binding (DPoP, mTLS): incorrectly implemented allows replay from other clients
Hunt: Identifying JWT Usage
- Check
Authorization: Bearer <token>headers in all requests - Look for cookies containing JWT structures (
eyJ...) - Examine browser local/session storage
- Decode the token at jwt.io or via BurpSuite JWT extension, inspect claims and header parameters
- Note any
kid,jku,jwk,x5ufields in the header, these are attack surfaces
