The file upload function in the "QWKalkulation" tool of baltic-it TOPqw Webportal v1.35.287.1 (fixed in version 1.35.291), in /Apps/TOPqw/QWKalkulation/QWKalkulation.aspx, is vulnerable to Cross-Site Scripting (XSS). To exploit the persistent XSS vulnerability, an attacker has to be authenticated to the application that uses the "TOPqw Webportal" as a software. When authenticated, the attacker can persistently place the malicious JavaScript code in the "QWKalkulation" menu.'