Possibility to load a template outside a configured directory when using the filesystem loader

Description

Under some circumstances, the sandbox security checks are not run which allows user-contributed templates to bypass the sandbox restrictions.

The security issue happens when all these conditions are met:

The sandbox is disabled globally; The sandbox is enabled via a sandboxed include() function which references a template name (like included.twig) and not a Template or TemplateWrapper instance; The included template has been loaded before the include() call but in a non-sandbox context (possible as the sandbox has been globally disabled).

Resolution

The patch ensures that the sandbox security checks are always run at runtime.

Credits

We would like to thank Fabien Potencier for reporting and fixing the issue.