Securing Node.js: Preventing Prototype Pollution

Prototype Pollution occurs when an attacker injects properties into Object.prototype, affecting all objects in the application; mitigate via input validation and using Object.create(null).

Vulnerable code often involves recursive merging or deep cloning of user-controlled JSON. If an attacker sends { "__proto__": { "admin": true } }, and the code merges this into an object, every object in the runtime will now have an admin property. Mitigation includes: 1. Using Map for user data, 2. Freezing the prototype with Object.freeze(Object.prototype), 3. Using schema validation (Joi/Zod) to strip forbidden keys like __proto__ or constructor.