Fix Prototype Pollution

[alromh87]

📊 Metadata *

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

Bounty URL: https://www.huntr.dev/bounties/1-npm-y18n

⚙️ Description *

Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects.
JavaScript allows all Object attributes to be altered, including their magical attributes such as proto.
An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values.
Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain.

💻 Technical Description *

Fixed by avoid setting magical attributes.

Note that in this case path is not expanded so constructor.prototype would not cause prototype pollution so filtering this magical attributes is not needed

🐛 Proof of Concept (PoC) *

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

🔥 Proof of Fix (PoF) *

After fix execution will block prototype pollution and throw an exception

👍 User Acceptance Testing (UAT)

After fix functionality is unafected

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