Webmin before 1.860 has XSS with resultant remote code execution. Under the 'Others/File Manager' menu, there is a 'Download from remote URL' option to download a file from a remote server. After setting up a malicious server, one can wait for a file download request and then send an XSS payload that will lead to Remote Code Execution, as demonstrated by an OS command in the value attribute of a name='cmd' input element.
Multiple Cross-site scripting (XSS) vulnerabilities in Webmin before 1.850 allow remote attackers to inject arbitrary web script or HTML via the sec parameter to view_man.cgi, the referers parameter to change_referers.cgi, or the name parameter to save_user.cgi. NOTE: these issues were not fixed in 1.840.