rspec/rules/S2245/javascript/rule.adoc

Using pseudorandom number generators (PRNGs) is security-sensitive. For example, it has led in the past to the following vulnerabilities:

* http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2013-6386[CVE-2013-6386]
* http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-3419[CVE-2006-3419]
* http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-4102[CVE-2008-4102]

When software generates predictable values in a context requiring unpredictability, it may be possible for an attacker to guess the next value that will be generated, and use this guess to impersonate another user or access sensitive information.


As the ``++Math.random()++`` function relies on a weak pseudorandom number generator, this function should not be used for security-critical applications or for protecting sensitive data. In such context, a cryptographically strong pseudorandom number generator (CSPRNG) should be used instead.

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== Recommended Secure Coding Practices

* Use a cryptographically strong pseudorandom number generator (CSPRNG) like ``++crypto.getRandomValues()++``.
* Use the generated random values only once.
* You should not expose the generated random value. If you have to store it, make sure that the database or file is secure.

== Sensitive Code Example

----
const val = Math.random(); // Sensitive
// Check if val is used in a security context.
----

== Compliant Solution

----
// === Client side ===
const crypto = window.crypto || window.msCrypto;
var array = new Uint32Array(1);
crypto.getRandomValues(array); // Compliant for security-sensitive use cases

// === Server side ===
const crypto = require('crypto');
const buf = crypto.randomBytes(1); // Compliant for security-sensitive use cases
----

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== Comments And Links
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