GHSA-pxm6-mhxr-q4mj: Grav Vulnerable to Privilege Escalation via Missing Server-Side Validation of groups/access
Bug Report: Registration Privilege Escalation via Missing Server-Side Validation of groups/accessSummaryThe `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.29Root CauseIn `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**: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: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**.PreconditionRegistration must be enabled with `groups` and/or `access` in the configured allowed fields: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 ConceptMalicious registration request (unauthenticated):Resulting account file (`user/accounts/attacker.yaml`):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 warningEnvironmentGrav Core: 1.8.0-beta.29Login Plugin: 3.8.0PHP: 8.4.11CreditsJonathan 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.
CVSS v3.1: 9.4