REDAXO is a PHP-based content management system. Prior to 5.21.2, rex_list::getSortColumn() in redaxo/src/core/lib/list.php accepts the sort request parameter without checking whether setColumnSortable() registered the requested column. An authenticated backend user can make prepareQuery() add an escaped but unauthorized ORDER BY identifier, allowing error-based enumeration of columns in joined tables and ordering by unselected sensitive fields such as rex_user.password. This issue is fixed in version 5.21.2.