# Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG) (CWE-338)

The product uses a Pseudo-Random Number Generator (PRNG) in a security context, but the PRNG's algorithm is not cryptographically strong.

- Prevalence: High Frequently exploited
- Impact: High 2 high-severity rules
- Prevention: Documented 4 fix examples

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

## Description

When a non-cryptographic PRNG is used in a security context (such as generating session tokens or cryptographic keys), an attacker may be able to predict its output and compromise the security mechanism.

## Prevention

Prevention strategies for Weak PRNG based on 4 Shoulder detection rules.

### Key Practices

- Use of Math

### Go

Use crypto/rand instead of math/rand for security-sensitive values

### Node.js

Use crypto.randomBytes() or crypto.randomUUID() for security-sensitive random values

### Python

Use the secrets module for tokens, passwords, and all security-sensitive randomness

Use the secrets module instead of random for security-sensitive operations

## Warning Signs

- [HIGH] math/rand used for security-sensitive random values
- [HIGH] Math.random() used for security-sensitive operation: ...
- [HIGH] use of Math
- [MEDIUM] use of insecure random number generators (random module) for
security-critical operations
- [MEDIUM] use of the random module for security-sensitive operations like
tokens, passwords, or cryptographic 

## Consequences

- Bypass Protection Mechanism
- Gain Privileges

## Mitigations

- Use cryptographically secure random number generators (CSPRNGs)
- In JavaScript, use crypto.getRandomValues() or crypto.randomUUID()
- In Python, use secrets module instead of random

## Detection

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

## Rules by Language

### Python (2 rules)

- **Insecure Random Number Generation** [MEDIUM]: Detects use of insecure random number generators (random module) for
security-critical operations. Use secrets module or os.urandom() for
cryptographic randomness (tokens, passwords, keys, nonces).
  - Remediation: Use the secrets module for tokens, passwords, and security-sensitive operations.

```python
import secrets

# Generate secure token
token = secrets.token_urlsafe(32)

# Generate secure hex token
reset_token = secrets.token_hex(32)

# Generate secure bytes for keys/salt
key = secrets.token_bytes(32)
```

Learn more: https://shoulder.dev/learn/python/cwe-338/insecure-randomness
- **Cryptographically Weak Random Number Generation** [MEDIUM]: Detects use of the random module for security-sensitive operations like
tokens, passwords, or cryptographic keys. The random module is not
cryptographically secure. Use the secrets module instead.
  - Remediation: Use the secrets module instead of random for security-sensitive operations.

```python
import secrets

token = secrets.token_hex(32)
api_key = secrets.token_urlsafe(32)

# For passwords:
import string
alphabet = string.ascii_letters + string.digits
password = ''.join(secrets.choice(alphabet) for _ in range(12))
```

Learn more: https://shoulder.dev/learn/python/cwe-338/weak-random

### Go (1 rules)

- **Weak Random Number Generation for Security** [HIGH]: Uses math/rand for security tokens, keys, or session IDs instead of crypto/rand.
  - Remediation: Use crypto/rand for all security-sensitive random values.

```go
import "crypto/rand"

token := make([]byte, 32)
if _, err := rand.Read(token); err != nil {
    return err
}
```

Learn more: https://shoulder.dev/learn/go/cwe-338/weak-random

### Javascript (1 rules)

- **Weak Random Number Generation in Security Context** [HIGH]: Detects use of Math.random() for security-sensitive operations like generating
tokens, session IDs, or cryptographic keys. Math.random() is not cryptographically
secure and can be predicted by attackers.
  - Remediation: Replace Math.random() with cryptographically secure alternatives.

### Typescript (1 rules)

- **Weak Random Number Generation in Security Context** [HIGH]: Detects use of Math.random() for security-sensitive operations like generating
tokens, session IDs, or cryptographic keys. Math.random() is not cryptographically
secure and can be predicted by attackers.
  - Remediation: Replace Math.random() with cryptographically secure alternatives.