WFTPD and WFTPD Pro 2.41 allows local users to cause a denial of service by executing the RENAME TO (RNTO) command before a RENAME FROM (RNFR) command.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2000-0644
http://www.securityfocus.com/templates/archive.pike?list=1&msg=E13BvU6-0007d8-00%40dwarf.box.sk