GetSimple CMS: Authenticated Stored Local File Inclusion (LFI) via page "template" field

GetSimple CMS is a content management system (CMS), and GetSimple CMS CE is the community edition of that CMS. In versions 3.3.22 and prior, an authenticated user with page-editing rights can store an arbitrary filesystem path in a page's template attribute. On the public front-end, this value is passed unsanitized to a PHP include() when the page is rendered. Because the include path is never confined, this allows directory-traversal Local File Inclusion: arbitrary local files are included (and, if they contain PHP, executed) when any visitor requests the page. At time of publication, there are no publicly available patches.