Craft is a platform for creating digital experiences. Versions 5.0.0-RC1 through 5.8.20 and 4.0.0-RC1 through 4.16.16 are vulnerable to potential authenticated Remote Code Execution via Twig SSTI. For this to work, users must have administrator access to the Craft Control Panel, and allowAdminChanges must be enabled, which is against Craft CMS recommendations for any non-dev environment. Alternatively, a non-administrator account with allowAdminChanges disabled can be used, provided access to the System Messages utility is available. It is possible to craft a malicious payload using the Twig map filter in text fields that accept Twig input under Settings in the Craft control panel or using the System Messages utility, which could lead to a RCE. Users should update to the patched versions (5.8.21 and 4.16.17) to mitigate the issue.
Weakness
The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Craft_cms | Craftcms | 4.0.0.1 (including) | 4.16.17 (excluding) |
| Craft_cms | Craftcms | 5.0.1 (including) | 5.8.21 (excluding) |
| Craft_cms | Craftcms | 4.0.0 (including) | 4.0.0 (including) |
| Craft_cms | Craftcms | 4.0.0-rc1 (including) | 4.0.0-rc1 (including) |
| Craft_cms | Craftcms | 4.0.0-rc2 (including) | 4.0.0-rc2 (including) |
| Craft_cms | Craftcms | 4.0.0-rc3 (including) | 4.0.0-rc3 (including) |
| Craft_cms | Craftcms | 5.0.0 (including) | 5.0.0 (including) |
| Craft_cms | Craftcms | 5.0.0-rc1 (including) | 5.0.0-rc1 (including) |
Extended Description
Many web applications use template engines that allow developers to insert externally-influenced values into free text or messages in order to generate a full web page, document, message, etc. Such engines include Twig, Jinja2, Pug, Java Server Pages, FreeMarker, Velocity, ColdFusion, Smarty, and many others - including PHP itself. Some CMS (Content Management Systems) also use templates. Template engines often have their own custom command or expression language. If an attacker can influence input into a template before it is processed, then the attacker can invoke arbitrary expressions, i.e. perform injection attacks. For example, in some template languages, an attacker could inject the expression “{{7*7}}” and determine if the output returns “49” instead. The syntax varies depending on the language. In some cases, XSS-style attacks can work, which can obscure the root cause if the developer does not closely investigate the root cause of the error. Template engines can be used on the server or client, so both “sides” could be affected by injection. The mechanisms of attack or the affected technologies might be different, but the mistake is fundamentally the same.