Directory traversal vulnerability in Nexgen FTP Server before 2.2.3.23 allows remote authenticated users to read or list arbitrary files via (1) "..", (2) "\..\" (backslash dot dot), or (3) "/../" sequences in (a) RETR (get), (b) NLST (ls), (c) LIST (ls), (d) RNFR, or (e) RNTO FTP commands.
https://exchange.xforce.ibmcloud.com/vulnerabilities/15594
http://www.securityfocus.com/bid/9970
http://www.nexgenserver.com/cgi-bin/loadframe2.cgi?/History.html