October is a Content Management System (CMS) and web platform to assist with development workflow. An authenticated backend user with the `editor.cms_pages`, `editor.cms_layouts`, or `editor.cms_partials` permissions who would normally not be permitted to provide PHP code to be executed by the CMS due to `cms.safe_mode` being enabled can write specific Twig code to escape the Twig sandbox and execute arbitrary PHP. This issue has been patched in 3.4.15.

October CMS safe mode bypass using Twig sandbox escape