REDAXO CMS is vulnerable to Reflected XSS in Mediapool Info Banner via args[types]

Summary

A reflected Cross-Site Scripting (XSS) vulnerability exists in the Mediapool view where the request parameter args[types] is rendered into an info banner without HTML-escaping. This allows arbitrary JavaScript execution in the backend context when an authenticated user visits a crafted link while logged in.

Details

Control Flow:

1. redaxo/src/addons/mediapool/pages/index.php reads args via rex_request('args', 'array') and passes them through as $argUrl to media.list.php.
2. redaxo/src/addons/mediapool/pages/media.list.php injects $argUrl['args']['types'] into an HTML string without escaping:

if (!empty($argUrl['args']['types'])) {
    echo rex_view::info(rex_i18n::msg('pool_file_filter') . ' <code>' . $argUrl['args']['types'] . '</code>');
}

PoC

1. Log into the REDAXO backend.
2. While authenticated, open a crafted URL like: <host>/index.php?page=mediapool/media&args[types]="><img+src%3Dx+onerror%3Dalert%28document.domain%29>
3. The info banner displays the unescaped value and activates the injected onerror handler, which opens an alert pop-up.

Impact

Arbitrary JavaScript execution in the backend, enabling theft of session cookies, CSRF tokens, or other sensitive data, and allowing an attacker to perform any administrative actions on behalf of the affected user.