Vulnerability Instance

Prototype Pollution in hoek
Versions of `hoek` prior to 4.2.1 and 5.0.3 are vulnerable to prototype pollution.

The `merge` function, and the `applyToDefaults` and `applyToDefaultsWithShallow` functions which leverage `merge` behind the scenes, are vulnerable to a prototype pollution attack when provided an _unvalidated_ payload created from a JSON string containing the `__proto__` property.

This can be demonstrated like so:

```javascript
var Hoek = require('hoek');
var malicious_payload = '{"__proto__":{"oops":"It works !"}}';

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

This type of attack can be used to overwrite existing properties causing a potential denial of service.