Unrestricted file upload vulnerability in the DownloadsPlus module in PHP-Nuke allows remote attackers to execute arbitrary code by uploading a file with (1) .htm, (2) .html, or (3) .txt extensions, then accessing it via a direct request to the file.  NOTE: the provenance of this information is unknown; the details are obtained solely from third party information.  NOTE: it is unclear how allowing the upload of .html or .txt files supports arbitrary code execution; this might be legitimate functionality.