AdonisJS is a TypeScript-first web framework. From 10.1.3 until 10.1.5 and 11.0.3, AdonisJS @adonisjs/bodyparser incompletely fixed CVE-2026-25754 because nested multipart field payloads such as user.__proto__.polluted and constructor.prototype still caused lodash _.set() via @poppinss/utils to create plain intermediate objects and pollute Object.prototype. This issue is fixed in versions 10.1.5 and 11.0.3.

Affected: npm: @adonisjs/bodyparser

### Summary

The fix for [GHSA-f5x2-vj4h-vg4c](https://github.com/adonisjs/core/security/advisories/GHSA-f5x2-vj4h-vg4c) / CVE-2026-25754 introduced in commit [`40e1c71`](https://github.com/adonisjs/bodyparser/commit/40e1c71f958cffb74f6b91bed6630dca979062ed) is incomplete and can be bypassed through nested prototype pollution payloads.

The original patch replaced the internal `FormFields` storage object with `Object.create(null)`, preventing direct payloads such as `__proto__.polluted`. However, payloads containing a non-dangerous segment before `__proto__` or `constructor.prototype`, such as `user.__proto__.polluted`, still lead to `Object.prototype` pollution.

This issue is exploitable remotely through a single unauthenticated `multipart/form-data` request using the default configuration.

### Affected versions

- `>= 10.1.3 < 10.1.5` - `>= 11.0.0-next.9 < 11.0.3`

### Details

The regression tests added by the original fix only covered direct payloads such as:

- `__proto__.polluted` - `constructor.prototype.polluted`

These payloads are blocked because the root object no longer inherits from `Object.prototype`.

However, lodash `_.set()` (via `@poppinss/utils`) still creates intermediate objects using plain `{}` values. Once a normal segment is encountered, subsequent `__proto__` or `constructor.prototype` segments regain access to `Object.prototype`.

### Impact

An unauthenticated attacker can remotely pollute `Object.prototype` on any route accepting multipart/form-…