REDAXO is a PHP-based content management system. Prior to 5.21.2, rex_api_install_package_update in redaxo/src/addons/install/lib/api/api_package_update.php inherits the false default from rex_api_function::requiresCsrfProtection() instead of requiring a CSRF token. An unauthenticated attacker can cause a logged-in administrator's browser to request a selected package update from the configured REDAXO package server, changing installed addon code or disrupting the site without the administrator's intent. This issue is fixed in version 5.21.2.