Orthanc server prior to version 1.5.8 does not enable basic authentication by default when remote access is enabled. This could result in unauthorized access by an attacker.
A XSS payload can be uploaded as a DICOM study and when a user tries to view the infected study inside the Osimis WebViewer the XSS vulnerability gets triggered. If exploited, the attacker will be able to execute arbitrary JavaScript code inside the victim's browser.