Cross-site scripting (XSS) vulnerability in MediaWiki before 1.16.4, when Internet Explorer 6 or earlier is used, allows remote attackers to inject arbitrary web script or HTML via an uploaded file accessed with a dangerous extension such as .html located before a ? (question mark) in a query string, in conjunction with a modified URI path that has a %2E sequence in place of the . (dot) character. NOTE: this vulnerability exists because of an incomplete fix for CVE-2011-1578.
https://bugzilla.redhat.com/show_bug.cgi?id=696360
http://www.debian.org/security/2011/dsa-2366
http://openwall.com/lists/oss-security/2011/04/18/5
http://lists.wikimedia.org/pipermail/mediawiki-announce/2011-April/000097.html