Prototype pollution attack (extend)

I would like to report prototype pollution in extend It allows an attacker to inject properties on Object.prototype. # Module **module name:** extend **version:** 3.0.1 **npm page:** `https://www.npmjs.com/package/extend` ## Module Description `node-extend` is a port of the classic extend() method from jQuery. It behaves as you expect. It is simple, tried and true. > **Note**: The github project is called `node-extend` but the NPM package is just `extend` ## Module Stats 7M downloads in the last week # Vulnerability ## Vulnerability Description This is a variant of this vulnerability: https://hackerone.com/reports/310443 The `extend` function can be tricked into adding or modifying properties of the Object prototype. These properties will be present on all objects. ## Steps To Reproduce: Craft an object of form `{__proto__: {...}}` and send it to `extend(true, {}, ...)`. ```javascript let extend = require('extend'); let payload = JSON.parse('{"__proto__": {"isAdmin": true}}'); extend(true, {}, payload); console.log({}.isAdmin); // true ``` # Wrap up - I contacted the maintainer to let them know: [N] - I opened an issue in the related repository: [N] ## Impact Denial of service, possibly more depending on the application. See https://hackerone.com/reports/310443