CVE-2020-28277: dset vulnerable to prototype pollution

Overview

Prototype pollution vulnerability in 'dset' versions 1.0.0 through 2.0.1 allows attacker to cause a denial of service and may lead to remote code execution.

Details

The NPM module 'dset' can be abused by Prototype Pollution vulnerability since the function ‘export ()' did not check for the type of object before assigning value to the property. Due to this flaw an attacker could create a non-existent property or able to manipulate the property which leads to Denial of Service or potentially Remote code execution.

PoC

The export function accepts three arguments obj, keys, val. Due to the absence of validation, at values passed into keys, val arguments, an attacker can supply a malicious value by adjusting the keys value to include the __proto__ property. Since there is no validation before assigning property to check whether the assigned keys is the Object's own property or not, the property isAdmin will be directly be assigned to the empty obj({}) thereby polluting the Object prototype. Later in the code, if there is a check to validate isAdmin the valued would be substituted as "true" as it had been polluted.

const dset = require('dset');
var obj = {}
console.log("Before : " + obj.isAdmin);
dset(obj, '__proto__.polluted', true);
console.log("After : " + obj.polluted);