CVE-2026-33157

EPSS 0.10%

Craft CMS is Vulnerable to Authenticated Remote Code Execution via Malicious Attached Behavior

Published: 3/24/2026Modified: 3/25/2026

Description

## 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(array_map( 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(EVENT_DEFINE_NATIVE_FIELDS)` 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. `call_user_func([ConsoleProcessus::class, 'execute'], $command)` -> `shell_exec($command)` ### Prerequisites - A user account with control panel access

Affected packages (1)

CVSS scores

SourceVersionSeverityVector
osvCVSS 4.0—CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

References (7)