administrator/components/com_media/helpers/media.php in the media manager in Joomla! 2.5.x before 2.5.14 and 3.x before 3.1.5 allows remote authenticated users or remote attackers to bypass intended access restrictions and upload files with dangerous extensions via a filename with a trailing . (dot), as exploited in the wild in August 2013.
https://github.com/joomla/joomla-cms/commit/fa5645208eefd70f521cd2e4d53d5378622133d8
https://github.com/joomla/joomla-cms/commit/1ed07e257a2c0794ba19e864f7c5101e7e8c41d2
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-5416
http://www.kb.cert.org/vuls/id/639620
http://www.exploit-db.com/exploits/27610
http://seclists.org/oss-sec/2013/q3/486
http://seclists.org/oss-sec/2013/q3/484
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31626
http://developer.joomla.org/security/563-20130801-core-unauthorised-uploads.html