Zen Cart 1.5.6d allows reflected XSS via the main_page parameter to includes/templates/template_default/common/tpl_main_page.php or includes/templates/responsive_classic/common/tpl_main_page.php.
Zen-cart
CVE-2021-3291
Zen Cart 1.5.7b allows admins to execute arbitrary OS commands by inspecting an HTML radio input element (within the modules edit page) and inserting a command.