Prototype pollution attack (defaults-deep / constructor.prototype)

I would like to report a prototype pollution vulnerability in defaults-deep. It allows an attacker to inject properties on Object.prototype. # Module **module name:** defaults-deep **version:** 0.2.4 **npm page:** `https://www.npmjs.com/package/defaults-deep` ## Module Description Like `extend` but recursively copies only the missing properties/values to the target object. ## Module Stats 6,659 downloads in the last week # Vulnerability ## Vulnerability Description This is a variant of this vulnerability: https://hackerone.com/reports/310443 The `defaults-deep` package 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 `{constructor: {prototype: {...}}}` and send it to `defaults-deep`: ```javascript var defaultsDeep = require('defaults-deep'); var payload = JSON.parse('{"constructor": {"prototype": {"isAdmin": true}}}'); defaultsDeep({}, 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