# Use of a Broken or Risky Cryptographic Algorithm (CWE-327)

The product uses a broken or risky cryptographic algorithm or protocol.

**Stack:** JavaScript

- Prevalence: 高 頻繁に悪用される
- Impact: ハイ 3 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

Cryptographic algorithms are the backbone of modern information security. Using algorithms that have known weaknesses, such as MD5 or DES, can make it trivial for attackers to defeat the protection.

## Prevention

2 件の Shoulder 検出ルールに基づく Broken Cryptographic Algorithm の予防策。

### JavaScript

Always specify allowed algorithms when verifying JWT tokens

Use SHA-256+ for hashing, AES-256-GCM for encryption, and bcrypt for passwords

## Warning Signs

- [HIGH] jwt.verify() without algorithm specification allows 'none' algorithm attack
- [HIGH] JWT verification without explicit algorithm specification, allowing "none" algorithm attacks that by
- [HIGH] use of weak or broken cryptographic algorithms for hashing passwords
or sensitive data

## Consequences

- アプリケーションデータの読み取り
- 保護メカニズムの回避

## Mitigations

- 対称暗号には AES-256 を使用する
- 非対称暗号には RSA-2048 以上または ECDSA を使用する
- ハッシュには SHA-256 または SHA-3 を使用する

## Detection

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

## Rules by Language

### Javascript (2 rules)

- **JWT Algorithm Confusion Attack** [HIGH]: Detects JWT verification without explicit algorithm specification, allowing "none" algorithm attacks that bypass authentication.
  - Remediation: Always specify allowed algorithms when verifying JWT tokens.
Example: jwt.verify(token, secret, { algorithms: ['RS256'] })
- **Use of Weak Cryptographic Algorithm** [HIGH]: Detects use of weak or broken cryptographic algorithms for hashing passwords
or sensitive data.

**Weak algorithms detected:**
- **MD5**: Cryptographically broken, vulnerable to collision attacks
- **SHA1**: Deprecated, vulnerable to collision attacks
- **DES/3DES**: Weak block cipher with small key size
- **RC4**: Stream cipher with known vulnerabilities

**Impact:**
- Password hashes can be cracked using rainbow tables or brute force
- Data encrypted with weak algorithms can be decrypted by at
  - Remediation: Use bcrypt/argon2 for passwords, SHA-256+ for hashing, and AES-256-GCM for encryption.

```javascript
const bcrypt = require('bcrypt');
const hash = await bcrypt.hash(password, 12);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-327/weak-crypto-algorithm

### Typescript (2 rules)

- **JWT Algorithm Confusion Attack** [HIGH]: Detects JWT verification without explicit algorithm specification, allowing "none" algorithm attacks that bypass authentication.
  - Remediation: Always specify allowed algorithms when verifying JWT tokens.
Example: jwt.verify(token, secret, { algorithms: ['RS256'] })
- **Use of Weak Cryptographic Algorithm** [HIGH]: Detects use of weak or broken cryptographic algorithms for hashing passwords
or sensitive data.

**Weak algorithms detected:**
- **MD5**: Cryptographically broken, vulnerable to collision attacks
- **SHA1**: Deprecated, vulnerable to collision attacks
- **DES/3DES**: Weak block cipher with small key size
- **RC4**: Stream cipher with known vulnerabilities

**Impact:**
- Password hashes can be cracked using rainbow tables or brute force
- Data encrypted with weak algorithms can be decrypted by at
  - Remediation: Use bcrypt/argon2 for passwords, SHA-256+ for hashing, and AES-256-GCM for encryption.

```javascript
const bcrypt = require('bcrypt');
const hash = await bcrypt.hash(password, 12);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-327/weak-crypto-algorithm