# 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.

**Stack:** Go

- Prevalence: 高 頻繁に悪用される
- Impact: ハイ 2 件の重大度ハイのルール
- Prevention: 文書化済み 4 件の修正例

**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

1 件の Shoulder 検出ルールに基づく Weak PRNG の予防策。

### Go

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

## Warning Signs

- [HIGH] math/rand used for security-sensitive random values

## Consequences

- 保護メカニズムの回避
- 権限の取得

## Mitigations

- 暗号学的に安全な乱数生成器 (CSPRNG) を使用する
- JavaScript では crypto.getRandomValues() または crypto.randomUUID() を使用する
- Python では random ではなく secrets モジュールを使用する

## Detection

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

## Rules by Language

### 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