Summary

A Remote Code Execution (RCE) vulnerability exists in Craft CMS 5.x and 4.x that bypasses the security fixes for GHSA-7jx7-3846-m7w7 and GHSA-255j-qw47-wjh5. This vulnerability can be exploited by any authenticated user with control panel access.

The existing patches add cleanseConfig() to assembleLayoutFromPost() and various FieldsController actions to strip Yii2 behavior/event injection keys (as and on prefixed keys). However, the fieldLayouts parameter in ElementIndexesController::actionFilterHud() is passed directly to FieldLayout::createFromConfig() without any sanitization, enabling the same behavior injection attack chain.

Impact

- Attack Type: Remote Code Execution (RCE) - Authentication Required: Authenticated user with control panel access (accessCp permission)

Vulnerability Details

Root Cause

In ElementIndexesController::actionFilterHud() (line 493-494), the fieldLayouts body parameter is passed to FieldLayout::createFromConfig() without cleanseConfig():

php // ElementIndexesController.php:485-494 if ($conditionConfig) { $conditionConfig = Component::cleanseConfig($conditionConfig); // conditionConfig IS cleansed $condition = $conditionsService->createCondition($conditionConfig); } else { $condition = $this->elementType()::createCondition(); }

if (!empty($fieldLayouts)) { // fieldLayouts is NOT cleansed! $condition->setFieldLayouts(arraymap( fn(array $config) => FieldLayout::createFromConfig($config), $fieldLayouts )); }

Note the inconsistency: conditionConfig is sanitized with cleanseConfig(), but fieldLayouts is not.

Attack Chain

1. Send a fieldLayouts array containing config with "as <name>" prefixed keys 2. FieldLayout::createFromConfig($config) -> new self($config) -> Model::construct($config) 3. App::configure($this, $config) processes each key 4. "as rce" key -> Component::set("as rce", $value) -> Yii::createObject($value) -> instantiates AttributeTypecastBehavior and attaches it to the FieldLayout 5. "on " key -> registers a wildcard event handler 6. parent::construct() -> init() -> setTabs([]) -> getAvailableNativeFields() -> trigger(EVENTDEFINENATIVEFIELDS) 7. The wildcard handler fires -> AttributeTypecastBehavior::beforeSave() -> typecastAttributes() 8. $this->owner->typecastBeforeSave -> resolved via Component::get() -> returns the command string from the behavior's own property 9. calluserfunc([ConsoleProcessus::class, 'execute'], $command) -> shellexec($command)

Prerequisites

- A user account with control panel access

Craft CMS is a content management system (CMS). From version 5.6.0 to before version 5.9.11, in src/controllers/EntryTypesController.php, the $settings array from parsestr is passed directly to Craft::configure() without Component::cleanseConfig(). This allows injecting Yii2 behavior/event handlers via "as" or "on" prefixed keys, the same attack vector as the original advisory. Craft control panel administrator permissions and allowAdminChanges must be enabled for this to work. This issue has been patched in version 5.9.11.