JavaScript Prototype Pollution Key Information Definition: - Prototype pollution is a vulnerability in JavaScript where an attacker can add or modify properties on an object's prototype. This can lead to unexpected behavior, logic errors, or additional attacks like cross-site scripting (XSS). Anatomy of Prototype Pollution: - Involves two phases: 1. Pollution: The attacker adds or modifies properties on an object's prototype. 2. Exploitation: Original application code accesses the polluted properties, leading to unexpected behavior. Pollution Sources: - Attackers can exploit the property to access the prototype object of any arbitrary object. Attackers may also use the constructor property pattern such as . Exploitation Targets: - API endpoints can be exploited to modify properties of built-in objects like . - Configuration objects (e.g., 's object) are often targets. Defenses Against Prototype Pollution: - Validate User Input: Use validators like or to ensure input data structure. - Node.js Flag: Use flag to disable . - Lock Down Built-in Objects: Freeze built-in objects to prevent modifications. - Avoid Prototype Lookups: Ensure properties exist on the object itself. - Create Null-Prototype Objects: Avoid prototype pollution with null prototype objects. Code Examples Conclusion Understanding prototype pollution and its defense mechanisms is crucial for securing JavaScript applications. The provided code examples and defense strategies can help developers mitigate the risks associated with this vulnerability.