# Improper Authentication (CWE-287)

When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

- Prevalence: High Frequently exploited
- Impact: Critical 2 critical-severity rules
- Prevention: Documented 2 fix examples

**OWASP:** Identification and Authentication Failures (A07:2021-Identification and Authentication Failures) - #7

## Description

Authentication is the process of determining if a claimed identity is correct. When authentication is insufficient or incorrect, attackers can assume the identity of legitimate users.

## Prevention

Prevention strategies for Improper Authentication based on 2 Shoulder detection rules.

### Node.js

Use jwt.verify() instead of jwt.decode() when assigning user identity

### Python

Use early returns for authentication failures and constant-time comparison

## Warning Signs

- [CRITICAL] when jwt
- [CRITICAL] authentication checks that can be bypassed due to missing return statements or weak boolean logic

## Consequences

- Gain Privileges
- Bypass Protection Mechanism
- Read Application Data

## Mitigations

- Use multi-factor authentication
- Use a vetted library or framework for authentication
- Implement proper password policies

## Detection

- Total rules: 2
- Critical: 2
- Languages: javascript, typescript, python

## Rules by Language

### Javascript (1 rules)

- **JWT Decode Used for User Identity (Authentication Bypass)** [CRITICAL]: Detects when jwt.decode() output is used for user identity, allowing complete authentication bypass since decode() does not verify signatures.
  - Remediation: Use jwt.verify() instead of jwt.decode() for authentication.

```javascript
const decoded = jwt.verify(token, process.env.JWT_SECRET, {
  algorithms: ['HS256']
});
req.user = decoded;
```

Learn more: https://shoulder.dev/learn/javascript/cwe-287/jwt-unverified-user-identity

### Typescript (1 rules)

- **JWT Decode Used for User Identity (Authentication Bypass)** [CRITICAL]: Detects when jwt.decode() output is used for user identity, allowing complete authentication bypass since decode() does not verify signatures.
  - Remediation: Use jwt.verify() instead of jwt.decode() for authentication.

```javascript
const decoded = jwt.verify(token, process.env.JWT_SECRET, {
  algorithms: ['HS256']
});
req.user = decoded;
```

Learn more: https://shoulder.dev/learn/javascript/cwe-287/jwt-unverified-user-identity

### Python (1 rules)

- **Authentication Bypass Vulnerability** [CRITICAL]: Detects authentication checks that can be bypassed due to missing return statements or weak boolean logic.
  - Remediation: Use early returns for authentication failures to prevent bypass.

```python
if not user or not check_password_hash(user.password_hash, password):
    return jsonify({'error': 'Invalid credentials'}), 401
```

Learn more: https://shoulder.dev/learn/python/cwe-287/authentication-bypass