The $args variable in addons/mediapool/pages/index.php in REDAXO 5.6.2 is not effectively filtered, because names are not restricted (only values are restricted). The attacker can insert XSS payloads via an index.php?page=mediapool/media&opener_input_field=&args[ substring.
In REDAXO before 5.6.3, a critical SQL injection vulnerability has been discovered in the rex_list class because of the prepareQuery function in core/lib/list.php, via the index.php?page=users/users sort parameter. Endangered was the backend and the frontend only if rex_list were used.