no-math-random-crypto

Type-unaware

Keywords: Math.random, insecure randomness, CSPRNG, token generation, session id, CWE-338, security, ESLint rule, LLM-optimized CWE: CWE-338 OWASP: A02:2021-Cryptographic Failures

Disallow Math.random() for cryptographic purposes (tokens, keys, secrets, salts, IVs)

Detects Math.random() used in a cryptographic context in Node.js code. Math.random() is a non-cryptographic PRNG: its output is predictable and must never seed tokens, keys, passwords, salts, IVs, nonces, or session identifiers. This rule is part of eslint-plugin-node-security and provides LLM-optimized error messages with fix suggestions.

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

Migrated from the deprecated standalone crypto plugin into eslint-plugin-node-security, which now ships every cryptography rule that plugin had — including this one.

Rule Details

The rule flags Math.random() only when the value flows into a cryptographic context, so benign randomness (shuffles, jitter, sampling, UI) does not trigger it. A context is treated as cryptographic when the result is:

assigned to a variable or property whose name matches token, key, secret, password, salt, iv, nonce, seed, session, csrf, otp, pin, auth, verify, etc.; or
returned from a function whose name suggests credential/token generation.

❌ Incorrect

function generateSessionToken() {
  return Math.random().toString(36).substring(2); // CWE-338: predictable token
}

const apiKey = Math.random().toString(36);

✅ Correct

import { randomBytes, randomUUID } from 'node:crypto';

function generateSessionToken() {
  return randomBytes(32).toString('hex');
}

const requestId = randomUUID();

// Non-crypto randomness is fine — not flagged
const j = Math.floor(Math.random() * deck.length);

Options

{
  "node-security/no-math-random-crypto": ["error", { "allowInTests": false }]
}

allowInTests (default false) — when true, allows Math.random() in *.test.* / *.spec.* files.

When Not To Use

If your codebase never uses Math.random() for anything security-sensitive and you want zero overhead, you can disable it — but the context-aware heuristic is designed to stay silent on non-crypto randomness, so leaving it on error is recommended.