An issue was discovered in Squiz Matrix CMS 5.5.0 prior to 5.5.0.3, 5.5.1 prior to 5.5.1.8, 5.5.2 prior to 5.5.2.4, and 5.5.3 prior to 5.5.3.3 where a user can trigger arbitrary unserialization of a PHP object from a packages/cms/page_templates/page_remote_content/page_remote_content.inc POST parameter during processing of a Remote Content page type. This unserialization can be used to trigger the inclusion of arbitrary files on the filesystem (local file inclusion), and results in remote code execution.