PHP Code Injection by malicious attribute in extends-tag in Smarty

Smarty is a template engine for PHP, facilitating the separation of presentation (HTML/CSS) from application logic. In affected versions template authors could inject php code by choosing a malicious file name for an extends-tag. Sites that cannot fully trust template authors should update asap. All users are advised to update. There is no patch for users on the v3 branch. There are no known workarounds for this vulnerability.