TWiki 01-Dec-2000 up to 4.0.3 allows remote attackers to bypass the upload filter and execute arbitrary code via filenames with double extensions such as ".php.en", ".php.1", and other allowed extensions that are not .txt. NOTE: this is only a vulnerability when the server allows script execution in the pub directory.
http://www.vupen.com/english/advisories/2006/2677
http://www.securityfocus.com/bid/18854
http://twiki.org/cgi-bin/view/Codev/SecurityAlertSecureFileUploads