GHSA-r5mx-6wc6-7h9w — dottie is vulnerable to Prototype Pollution bypass via non-first path segments in set() and transform()

Affected: npm: dottie

### Summary

dottie versions 2.0.4 through 2.0.6 contain an incomplete fix for CVE-2023-26132. The prototype pollution guard introduced in commit `7d3aee1` only validates the first segment of a dot-separated path, allowing an attacker to bypass the protection by placing `__proto__` at any position other than the first.

Both `dottie.set()` and `dottie.transform()` are affected.

### Details

The existing guard checks only `pieces[0] === '__proto__'`. When a path like `'a.__proto__.polluted'` is used, `pieces[0]` evaluates to `'a'`, not `'__proto__'`, so the guard is bypassed.

Inside the traversal loop, `current['__proto__'] = {}` triggers the `__proto__` setter, replacing the intermediate object's prototype. The final value is then written onto this new prototype.

**Important distinction:** This vulnerability does NOT pollute the global `Object.prototype`. It injects properties into a specific object's prototype chain. However, injected properties are invisible to `hasOwnProperty()` and `Object.keys()`, which makes them difficult to detect and can lead to authorization bypass in common coding patterns.

### PoC ```javascript const dottie = require('dottie');

// set() bypass const obj = {}; dottie.set(obj, 'session.__proto__.isAdmin', true); console.log(obj.session.isAdmin); // true console.log(({}).isAdmin); // undefined console.log(obj.session.hasOwnProperty('isAdmin')); // false

// transform() bypass const flat = { 'user.__…

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GHSA-r5mx-6wc6-7h9w — dottie is vulnerable to Prototype Pollution bypass via non-first path segments in set() and transform()