no-cryptojs-weak-random

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Keywords: crypto-js, WordArray.random, weak random, Math.random, CVE-2020-36732, CWE-338, ESLint rule CWE: CWE-338
CVE: CVE-2020-36732
OWASP: A02:2021-Cryptographic Failures

Disallow crypto-js WordArray.random() (CVE-2020-36732)

Detects usage of crypto-js WordArray.random() which used insecure Math.random() in versions prior to 3.2.1. This rule is part of eslint-plugin-node-security and provides LLM-optimized error messages.

🚨 Security rule | 💡 Provides suggestions | ⚠️ Set to error in recommended

Quick Summary

Aspect	Details
CWE Reference	CWE-338 (Weak PRNG)
CVE Reference	CVE-2020-36732
Severity	Critical (security vulnerability)
Auto-Fix	💡 Suggests crypto.randomBytes()
Category	Security
ESLint MCP	✅ Optimized for ESLint MCP integration
Best For	Projects using or migrating from crypto-js

Vulnerability and Risk

Vulnerability: In crypto-js versions prior to 3.2.1, CryptoJS.lib.WordArray.random() used JavaScript's Math.random() for generating random bytes. Math.random() is not cryptographically secure and produces predictable values.

Risk: Keys, IVs, salts, and tokens generated with this function are predictable. An attacker can reproduce the random values and decrypt data, forge signatures, or bypass authentication.

Rule Details

This rule detects:

CryptoJS.lib.WordArray.random()
WordArray.random()
CryptoJS.random()

Why This Matters

Risk	Impact	Solution
🎲 Predictable Random	Generated values can be reproduced	Use crypto.randomBytes()
🔑 Weak Keys/IVs	Encryption keys become guessable	Migrate to native CSPRNG
🔓 Token Forge	Session tokens can be predicted	Never use Math.random for crypto

Configuration

Option	Type	Default	Description
`allowInTests`	`boolean`	`false`	Allow in test files

{
  rules: {
    'node-security/no-cryptojs-weak-random': ['error', {
      allowInTests: false
    }]
  }
}

Examples

❌ Incorrect

import CryptoJS from 'crypto-js';

// Weak random - uses Math.random() in versions < 3.2.1
const salt = CryptoJS.lib.WordArray.random(16); // ❌ CVE-2020-36732

// Generating IV with weak random
const iv = WordArray.random(16); // ❌ Predictable IV

// Generating key material
const key = CryptoJS.lib.WordArray.random(32); // ❌ Weak key

✅ Correct

import crypto from 'node:crypto';

// Use cryptographically secure random bytes
const salt = crypto.randomBytes(16); // ✅ Uses OS CSPRNG

// Generating IV
const iv = crypto.randomBytes(16); // ✅ Secure

// Generating key material
const keyBytes = crypto.randomBytes(32); // ✅ Secure

// In browsers, use Web Crypto API
const browserRandom = new Uint8Array(16);
globalThis.crypto.getRandomValues(browserRandom); // ✅ Secure

CVE-2020-36732 Details

Affected Versions: crypto-js < 3.2.1
CVSS Score: 7.5 (High)
Attack Vector: Remote
Issue: Used Math.random() which has only 2^52 possible states

The Problem with Math.random()

// Math.random() internals (V8 example)
// Uses xorshift128+ with only 128 bits of state
// State can be reconstructed from ~5 outputs
// NOT suitable for cryptographic use

// DO NOT USE for crypto:
const weakKey = Array.from({ length: 32 }, () =>
  Math.floor(Math.random() * 256),
);

Security Impact

Vulnerability	CWE	OWASP	CVSS	Impact
Weak PRNG	338	A02:2021	7.5 High	Predictable crypto values
Insufficient Entropy	331	A02:2021	5.9 Medium	Key material weakness

Migration Guide

Phase 1: Audit

# Check crypto-js version
npm list crypto-js
# If < 3.2.1, vulnerable!

Phase 2: Replace

// Before (vulnerable)
import CryptoJS from 'crypto-js';
const random = CryptoJS.lib.WordArray.random(32);

// After (secure)
import crypto from 'node:crypto';
const random = crypto.randomBytes(32);

Phase 3: Remove crypto-js

npm uninstall crypto-js

no-cryptojs - Detect all crypto-js usage
prefer-native-crypto - Prefer native crypto

Known False Negatives

Aliased Imports

Why: Aliased references not tracked.

// ❌ NOT DETECTED
const rand = CryptoJS.lib.WordArray.random;
rand(16);

Mitigation: Search for all WordArray references.