NodeJS - proto & prototype Pollution

👉 Overview

👀 What ?

Node.js prototype pollution is a vulnerability that occurs when properties of JavaScript 'prototype' objects are incorrectly processed within the codebase, which can lead to a wide range of security issues, from denial of service (DoS) to possibly remote code execution (RCE). The 'proto' is a property of an object that points to the 'prototype' of the constructor function that created the object.

🧐 Why ?

Understanding prototype pollution, particularly in Node.js, is crucial because it is a common vulnerability that can lead to serious security issues. It's important for developers to understand how to avoid introducing such vulnerabilities into their code, and for penetration testers to be able to identify and exploit them.

⛏️ How ?

To prevent prototype pollution, developers should avoid modifying objects' prototypes and use hasOwnProperty() method to verify that an object property is not from the prototype chain. For penetration testers, tools such as the 'prototype pollution gadgets' can be used to find potential vulnerabilities.

⏳ When ?

Prototype pollution vulnerabilities have been a concern in JavaScript and Node.js since their inception, due to the flexibility of the language. They continue to be a concern today, and are often found in widely used libraries.

⚙️ Technical Explanations

In JavaScript, all objects implicitly have a 'prototype' property, which is used for inheritance. When a new object is created, it inherits the properties of its constructor's prototype. The 'proto' property is a reference to this inherited prototype. Prototype pollution occurs when these properties are modified, typically through the addition of new properties, in a way that wasn't intended by the developer. This can lead to unexpected behavior in the application, including security vulnerabilities. For example, an attacker could add a property to an object's prototype that causes all objects created by that constructor to include a malicious function.