# Improper Verification of Cryptographic Signature (CWE-347)

The product does not verify, or incorrectly verifies, the cryptographic signature for data.

**Stack:** Python

- Prevalence: Alta Frecuentemente explotada
- Impact: Crítico 1 reglas de severidad crítica
- Prevention: Documentada 4 ejemplos de corrección

**OWASP:** Cryptographic Failures (A02:2021-Cryptographic Failures) - #2

## Description

Cryptographic signatures are used to verify the authenticity and integrity of data. When signature verification is missing or incorrectly implemented, attackers can forge or tamper with data.

## Prevention

Estrategias de prevención para Improper Signature Verification basadas en 2 reglas de detección de Shoulder.

### Python

Load JWT secret from environment and explicitly specify allowed algorithms

Always specify allowed algorithms explicitly when decoding JWT tokens

## Warning Signs

- [HIGH] JWT implementation has security vulnerabilities
- [HIGH] JWT security issues in FastAPI applications including:
- Weak or hardcoded secrets
- Missing algorit
- [CRITICAL] JWT tokens decoded without algorithm verification or accepting the 'none' algorithm, allowing token 

## Consequences

- Eludir mecanismo de protección
- Ejecutar código no autorizado
- Modificar datos de la aplicación

## Mitigations

- Verifica siempre las firmas antes de confiar en los datos
- Usa bibliotecas criptográficas bien probadas para la verificación de firmas
- Para JWT, verifica siempre la firma y valida el algoritmo

## Detection

- Total rules: 4
- Critical: 1
- Languages: python, go, javascript, typescript

## Rules by Language

### Python (2 rules)

- **FastAPI JWT Security Issues** [HIGH]: Detects JWT security issues in FastAPI applications including:
- Weak or hardcoded secrets
- Missing algorithm verification
- Insufficient token validation
- Insecure token storage patterns
  - Remediation: Load JWT secret from environment and explicitly specify the algorithm.

```python
from pydantic_settings import BaseSettings
from jose import jwt

class Settings(BaseSettings):
    SECRET_KEY: str
    ALGORITHM: str = "HS256"

settings = Settings()

def decode_token(token: str):
    return jwt.decode(token, settings.SECRET_KEY, algorithms=[settings.ALGORITHM])
```

Learn more: https://shoulder.dev/learn/python/cwe-347/jwt-security
- **JWT Algorithm Confusion Attack** [CRITICAL]: Detects JWT tokens decoded without algorithm verification or accepting the 'none' algorithm, allowing token forgery.
  - Remediation: Always specify allowed algorithms explicitly when decoding JWT tokens.

```python
payload = jwt.decode(token, SECRET_KEY, algorithms=['HS256'])
```

Learn more: https://shoulder.dev/learn/python/cwe-347/jwt-algorithm-confusion