The utilities function in all versions <= 0.3.0 of the merge-recursive node module can be tricked into modifying the prototype of Object when the attacker can control part of the structure passed to this function. This can let an attacker add or modify existing properties that will exist on all objects.

Affected: npm: merge-recursive

All versions of `merge-recursive` are vulnerable to Prototype Pollution. When malicious user input is merged with another object it allows the attacker to modify the prototype of Object via `__proto__` causing the addition or modification of an existing property.

Proof of concept:

```js var merge = require('merge-recursive').recursive; var malicious_payload = '{"__proto__":{"oops":"It works !"}}';

var a = {}; console.log("Before : " + a.oops); merge({}, JSON.parse(malicious_payload)); console.log("After : " + a.oops); ```

## Recommendation

There is currently no fix available.