Understanding Prototype Pollution

Prototype pollution is a vulnerability primarily discussed in the context of JavaScript, but it can affect any system using a prototype-based inheritance model. This vulnerability occurs when an attacker manipulates an object's prototype, affecting all instances of that object.

Key Points

• Prototype Pollution: A vulnerability where an attacker modifies an object's prototype, impacting all instances.
• JavaScript Context: Commonly discussed in JavaScript due to its prototype-based inheritance.
• Impact: Can lead to security breaches, including XSS, property injection, and DDoS attacks.

JavaScript Basics

Objects

Objects in JavaScript act as containers that hold various pieces of information.

Classes

Classes serve as blueprints for creating multiple objects with similar structures and behaviors.

Prototypes

In JavaScript, every object links to a prototype object, forming a prototype chain.

Classes vs. Prototypes

Feature	Classes	Prototypes
Structure	Provide a clear, structured way to create objects.	Start with a simple object and add behaviors by linking to a prototype.
Inheritance	Objects share the same properties and methods.	Objects inherit behaviors through the prototype chain.
Ease of Use	Easier to understand and use.	More flexible but can be complex.

How Prototype Pollution Works

Prototype pollution is a vulnerability that arises when an attacker manipulates an object's prototype, impacting all instances of that object.

Example

// Base Prototype for Persons
let personPrototype = {
  introduce: function() {
    return `Hi, I'm ${this.name}.`;
  }
};

// Person Constructor Function
function Person(name) {
  let person = Object.create(personPrototype);
  person.name = name;
  return person;
}

// Creating an instance
let ben = Person('Ben');

// Attacker's Payload
ben.__proto__.introduce = function() {
  console.log("You've been hacked, I'm Bob");
}
console.log(ben.introduce());

You've been hacked, I'm Bob

Exploitation

Prototype pollution can be combined with other attacks:

• XSS (Cross-Site Scripting)
• Property Injection
• DDoS (Distributed Denial of Service)

Mitigation Measures

For Pentesters

• Input Fuzzing and Manipulation
• Context Analysis and Payload Injection
• CSP Bypass and Payload Injection
• Dependency Analysis and Exploitation
• Static Code Analysis

For Secure Code Developers

• Avoid Using __proto__
• Immutable Objects
• Encapsulation
• Use Safe Defaults
• Input Sanitisation
• Dependency Management
• Security Headers

Learn More

For more detailed information on prototype pollution and other cybersecurity topics, consider exploring resources such as OWASP and MDN Web Docs.