Microsoft SharePoint uses URLs with the same hostname and port number for a web site's primary files and individual users' uploaded files (aka attachments), which allows remote authenticated users to leverage same-origin relationships and conduct cross-site scripting (XSS) attacks by uploading HTML documents.
https://exchange.xforce.ibmcloud.com/vulnerabilities/46590
http://www.pomcor.com/whitepapers/file_sharing_security.pdf
http://archives.neohapsis.com/archives/bugtraq/2008-11/0058.html
http://archives.neohapsis.com/archives/bugtraq/2008-11/0056.html
http://archives.neohapsis.com/archives/bugtraq/2008-11/0055.html