Question 74

Question

How does prototype pollution occur and how can it be prevented?

Answer

What is Prototype Pollution?

Prototype pollution happens when malicious code alters the prototype chain of an object. This means attackers can add properties to built-in objects or user-defined classes, potentially overriding existing methods and functionalities with their own malicious code. This can lead to serious security breaches.

How it Occurs:

1. Uncontrolled User Input: The most common cause is accepting untrusted user input without proper sanitization. If an attacker can inject data into a property assignment where the target object's prototype chain is involved, they can introduce malicious code.

   Object.defineProperty(globalThis.__proto__, 'someProperty', {
       value: function() {  // Malicious code!
           console.log('Prototype polluted!'); 
       }
   });

2. Incorrect use of __proto__: Directly manipulating the __proto__ property can lead to unintended consequences and make objects vulnerable to pollution.

Consequences:

• Data Manipulation: Attackers can modify data stored in user-defined objects or built-in objects like Array, Object, etc.

• Code Execution: They can inject malicious code that runs when objects are created or used.

• Bypass Security Measures: Prototype pollution can undermine security mechanisms relying on trusted prototypes, leading to privilege escalation.

Prevention Strategies:

1. Sanitize User Input: Always validate and sanitize user input before using it in object creation or property assignments. Escape special characters and use whitelist approaches to restrict allowed values.

2. Avoid Direct __proto__ Manipulation: Instead of directly modifying the __proto__ property, rely on established methods for inheritance and class structures. Consider using libraries like Proxy for more controlled access to object properties.

3. Use Secure Frameworks/Libraries: Employ frameworks or libraries known for robust security practices that mitigate vulnerabilities like prototype pollution.

4. Regular Security Audits: Conduct regular security audits and penetration testing to identify potential weaknesses in your codebase.