Individual skill

web-prototype-pollution

JavaScript prototype pollution (client & server) → XSS, auth bypass, RCE via gadgets. Load on Node.js/JS apps that merge user objects: query/JSON parsing, `Object.assign`/deep-merge, lodash/jQuery.extend, config merges. Signals: __proto__, constructor.prototype in params, Node backend, client-side sinks.

skills/web/web-prototype-pollution/SKILL.md

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Last checked: Nov 7, 2026

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Repository stars (not skill ratings): 27
Repository last updated: Oct 14, 2026
License: MIT

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# Prototype pollution

## When it applies
A JS app merges attacker-controlled keys into an object without blocking `__proto__` /
`constructor` / `prototype`. Client-side or Node server-side. Impact needs a "gadget" — code
that later reads a polluted property.

## Why it works
In JS, every object shares `Object.prototype`. Writing `__proto__.x` via a vulnerable merge sets
`x` on *every* object. A later read of `obj.x` (that the dev assumed was undefined) now returns
your value — turning a config default, an HTML attribute, or a command option to your advantage.

## Method
1. **Find the sink**: params/JSON merged via deep-merge/`Object.assign`/lodash `merge`/`set`,