Grav is a file-based Web platform. Prior to 2.0.0-beta.2, the Login::register() method in the Login plugin accepts attacker-controlled groups and access fields from the registration POST data without server-side validation. When registration is enabled and groups or access are included in the configured allowed fields list, an unauthenticated user can self-register with admin.super privileges by injecting these fields into the registration request. This vulnerability is fixed in 2.0.0-beta.2.

Affected: Packagist: getgrav/grav

# Bug Report: Registration Privilege Escalation via Missing Server-Side Validation of groups/access

## Summary

The `Login::register()` method in the Login plugin accepts attacker-controlled `groups` and `access` fields from the registration POST data without server-side validation. When registration is enabled and `groups` or `access` are included in the configured allowed fields list, an unauthenticated user can self-register with `admin.super` privileges by injecting these fields into the registration request.

This is a missing server-side validation issue — the only defense is a config-level `fields` allowlist, which is an admin-facing setting, not a hardcoded security boundary.

## Affected Component

- **File:** `user/plugins/login/classes/Login.php`, lines 246-306 - **Method:** `Login::register()` - **Validation:** `Login::validateField()`, lines 363-432 - **Plugin:** Login Plugin 3.8.0 - **Grav:** 1.8.0-beta.29

## Root Cause

In `register()` (lines 254-267), the `groups` and `access` fields are only set to config defaults **if they are not already present in the input data**:

```php // Line 254-260 if (!isset($data['groups'])) { $groups = (array) $this->config->get('plugins.login.user_registration.groups', []); if (count($groups) > 0) { $data['groups'] = $groups; } }

// Line 262-267 if (!isset($data['access'])) { $access = (array) $this->config->get('plugins.login.user_registration.access.site', []); if (count($access) > 0) {…