The private filesystem in Drupal 5.x before 5.10 and 6.x before 6.4 trusts the MIME type sent by a web browser, which allows remote authenticated users to conduct cross-site scripting (XSS) attacks by uploading files containing arbitrary web script or HTML.
https://www.redhat.com/archives/fedora-package-announce/2008-September/msg00508.html
https://www.redhat.com/archives/fedora-package-announce/2008-September/msg00259.html
https://exchange.xforce.ibmcloud.com/vulnerabilities/44446
https://bugzilla.redhat.com/show_bug.cgi?id=459108
http://www.vupen.com/english/advisories/2008/2392
http://www.securityfocus.com/bid/30689
http://secunia.com/advisories/31825