Testing JWT Token Security

# Testing JWT Token Security

## When to Use

- During authorized penetration tests when the application uses JWT for authentication or authorization
- When assessing API security where JWTs are passed as Bearer tokens or in cookies
- For evaluating SSO implementations that use JWT/JWS/JWE tokens
- When testing OAuth 2.0 or OpenID Connect flows that issue JWTs
- During security audits of microservice architectures using JWT for inter-service authentication

## Prerequisites

- **Authorization**: Written penetration testing agreement for the target
- **jwt_tool**: JWT attack toolkit (`pip install jwt_tool` or `git clone https://github.com/ticarpi/jwt_tool.git`)
- **Burp Suite Professional**: With JSON Web Token extension from BApp Store
- **Python PyJWT**: For scripting custom JWT attacks (`pip install pyjwt`)
- **Hashcat**: For brute-forcing HMAC secrets (`apt install hashcat`)
- **jq**: For JSON processing
- **Target JWT**: A valid JWT token from the application

## Workflow

### Step 1: Decode and Analyze the JWT Structure

Extract and examine the header, payload, and signature components.

```bash
# Decode JWT parts (base64url decode)
JWT="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"

# Decode header
echo "$JWT" | cut -d. -f1 | base64 -d 2>/dev/null | jq .
# Output: {"alg":"HS256","typ":"JWT"}

# Decode payload
echo "$JWT" | cut -d. -f2 | base64 -d 2>/dev/null | jq .
# Output: {"sub":"1234567890","name":"John Doe","iat":1516239022}

# Using jwt_tool for comprehensive analysis
python3 jwt_tool.py "$JWT"

# Check for sensitive data in the payload:
# - PII (email, phone, address)
# - Internal IDs or database references
# - Role/permission claims
# - Expiration times (exp, nbf, iat)
# - Issuer (iss) and audience (aud)
```

### Step 2: Test Algorithm None Attack