GHSA-7jx7-3846-m7w7 Craft CMS Vulnerable to potential authenticated Remote Code Execution via malicious attached Behavior

• Packagist craftcms/cms: >= 5.0.0-RC1, < 5.8.22 → fixed in 5.8.22 • Packagist craftcms/cms: >= 4.0.0-RC1, < 4.16.18 → fixed in 4.16.18

Relationship to Previously Patched Vulnerability This vulnerability is in addition to the RCE vulnerability patched in GHSA-255j-qw47-wjh5. That advisory addressed a similar RCE vulnerability that affected two specific routes: • `/index.php?p=admin%2Factions%2Ffields%2Fapply-layout-element-settings` • `/index.php?p=admin%2Factions%2Ffields%2Frender-card-preview` This one addresses some additional endpoints that were not covered in the https://github.com/craftcms/cms/security/advisories/GHSA-255j-qw47-wjh5. The patched vulnerability used a malicious `AttributeTypecastBehavior` with a wildcard event listener (`"on *": "self::beforeSave"`) and `__construct()` syntax to trigger RCE via the `typecastBeforeSave` callback. The fix was implemented in commits: • 6e608a1 • 27f5588 • ec43c49 This vulnerability follows the same attack pattern (behavior injection via `"as "` syntax) but affects a different code path (`assembleLayoutFromPost()` in `Fields.php`) that was not patched in those commits. The attack vector uses `typecastAfterValidate` instead of `typecastBeforeSave` and does not require the wildcard event listener syntax, demonstrating that multiple entry points exist for this type of vulnerability. --- Executive Summary A Remote Code Execution (RCE) vulnerability exists in Craft CMS where the `assembleLayoutFromPost()` function in `src/services/Fields.php` fails to sanitize user-supplied configuration data before passing it to `Craft::createObject()`. This allows authenticated administrators to inject malicious Yii2 behavior configurations that execute arbitrary system commands on the server. This vulnerability represents an unpatched variant of the behavior injection vulnerability addressed in GHSA-255j-qw47-wjh5, affecting different endpoints through a separate code path. --- Vulnerability Details Attack Prerequisites • Authentication: Admin-level access required • Network Access: Access to admin panel (`/admin`) --- Location • File: `src/services/Fields.php` • Function: `assembleLayoutFromPost()` (lines 1125-1143) • Root Cause: Missing `cleanseConfig()` call on user-supplied `fieldLayout` POST parameter Vulnerable Code Path ```php // src/services/Fields.php:1125-1133 public function assembleLayoutFromPost(?string $namespace = null): FieldLayout { $paramPrefix = $namespace ? rtrim($namespace, '.') . '.' : ''; $request = Craft::$app->getRequest(); $config = JsonHelper::decode($request->getBodyParam("{$paramPrefix}fieldLayout")); // ... additional config values added ... $layout = $this->createLayout($config); // <-- No cleanseConfig() call! // ... } // src/services/Fields.php:1089-1093 public function createLayout(array $config): FieldLayout { $config['class'] = FieldLayout::class; return Craft::createObject($config); // <-- Untrusted data passed directly } ``` --- Attack Chain The exploitation leverages Yii2's object configuration system and behavior attachment mechanism: 1. Behavior Injection: Attacker includes `'as rce'` key in the `fieldLayout` JSON POST parameter 2. Object Creation: `Craft::createObject()` processes the config through Yii2's `BaseYii::configure()` 3. Behavior Attachment: Yii2's `Component::__set()` detects the `'as '` prefix and attaches the behavior 4. RCE Trigger: When `validate()` is called on the model, `EVENT_AFTER_VALIDATE` fires 5. Command Execution: `AttributeTypecastBehavior` calls the configured typecast function (`ConsoleProcessus::execute`) with the `uid` attribute value as the command RCE Gadget Chain ``` FieldLayout POST parameter → Craft::createObject() → Yii2 Component::__set() with 'as rce' key → AttributeTypecastBehavior attached → Model::validate() called → EVENT_AFTER_VALIDATE triggered → typecastAfterValidate → typecastAttributes() → call_user_func(['Psy\Readline\Hoa\ConsoleProcessus', 'execute'], $command) → Shell command execution ``` --- Affected Controllers The `assembleLayoutFromPost()` function is called by multiple admin controllers: | Controller | Action | Permission Required | |------------|--------|---------------------| | `TagsController` | `actionSaveTagGroup()` | Admin | | `CategoriesController` | `actionSaveGroup()` | Admin | | `EntryTypesController` | `actionSave()` | Admin | | `GlobalsController` | `actionSaveSet()` | Admin | | `VolumesController` | `actionSave()` | Admin | | `UsersController` | `actionSaveUserFieldLayout()` | Admin | | `AddressesController` | `actionSaveAddressFieldLayout()` | Admin | --- References • https://github.com/craftcms/cms/commit/395c64f0b80b507be1c862a2ec942eaacb353748 • GHSA-255j-qw47-wjh5 - Previously patched RCE vulnerability via behavior injection (affecting different endpoints) • CVE-2024-4990 - Related vulnerability that inspired the behavior injection attack pattern • Yii2 GHSA-gcmh-9pjj-7fp4 - Original Yii framework report (framework team declined to fix at framework level) ---