The get_allowed_mime_types function in wp-includes/functions.php in WordPress before 3.6.1 does not require the unfiltered_html capability for uploads of .htm and .html files, which might make it easier for remote authenticated users to conduct cross-site scripting (XSS) attacks via a crafted file.
http://www.debian.org/security/2013/dsa-2757
http://wordpress.org/news/2013/09/wordpress-3-6-1/