REDAXO before 5.21.3 contains a reflected cross-site scripting vulnerability in the backend media pool detail page, where the opener_link parameter is rendered without HTML escaping. Unauthenticated attackers can lure logged-in backend users with media permissions into clicking a crafted link. The injected script can then read the CSRF token and perform actions with the victim's permissions, including code execution via template or module edits when the victim is an administrator.