The core Upload module in Drupal 4.7.x before 4.7.8 and 5.x before 5.3 places the .html extension on a whitelist, which allows remote attackers to conduct cross-site scripting (XSS) attacks by uploading .html files.
https://www.redhat.com/archives/fedora-package-announce/2007-October/msg00328.html
https://exchange.xforce.ibmcloud.com/vulnerabilities/37274
http://www.vupen.com/english/advisories/2007/3546
http://www.securityfocus.com/bid/26119
http://secunia.com/advisories/27352