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

class MetasploitModule < Msf::Auxiliary
  include Msf::Exploit::Remote::Tcp

  def initialize(info = {})
    super(update_info(info,
      'Name'          => 'Modbus Client Utility',
      'Description'   => %q{
        This module allows reading and writing data to a PLC using the Modbus protocol.
        This module is based on the 'modiconstop.rb' Basecamp module from DigitalBond,
        as well as the mbtget perl script.
      },
      'Author'         =>
        [
          'EsMnemon <esm[at]mnemonic.no>', # original write-only module
          'Arnaud SOULLIE  <arnaud.soullie[at]solucom.fr>', # code that allows read/write
          'Alexandrine TORRENTS <alexandrine.torrents[at]eurecom.fr>', # code that allows reading/writing at multiple consecutive addresses
          'Mathieu CHEVALIER <mathieu.chevalier[at]eurecom.fr>'
        ],
      'License'        => MSF_LICENSE,
      'Actions'        =>
        [
          ['READ_COILS', { 'Description' => 'Read bits from several coils' } ],
          ['READ_REGISTERS', { 'Description' => 'Read words from several registers' } ],
          ['WRITE_COIL', { 'Description' => 'Write one bit to a coil' } ],
          ['WRITE_REGISTER', { 'Description' => 'Write one word to a register' } ],
          ['WRITE_COILS', { 'Description' => 'Write bits to several coils' } ],
          ['WRITE_REGISTERS', { 'Description' => 'Write words to several registers' } ]
        ],
      'DefaultAction' => 'READ_REGISTERS'
      ))

    register_options(
      [
        Opt::RPORT(502),
        OptInt.new('DATA_ADDRESS', [true, "Modbus data address"]),
        OptInt.new('NUMBER', [false, "Number of coils/registers to read (READ_COILS ans READ_REGISTERS modes only)", 1]),
        OptInt.new('DATA', [false, "Data to write (WRITE_COIL and WRITE_REGISTER modes only)"]),
        OptString.new('DATA_COILS', [false, "Data in binary to write (WRITE_COILS mode only) e.g. 0110"]),
        OptString.new('DATA_REGISTERS', [false, "Words to write to each register separated with a comma (WRITE_REGISTERS mode only) e.g. 1,2,3,4"]),
        OptInt.new('UNIT_NUMBER', [false, "Modbus unit number", 1]),
      ])

  end

  # a wrapper just to be sure we increment the counter
  def send_frame(payload)
    sock.put(payload)
    @modbus_counter += 1
    sock.get_once(-1, sock.def_read_timeout)
  end

  def make_payload(payload)
    packet_data = [@modbus_counter].pack("n")
    packet_data += "\x00\x00\x00" #dunno what these are
    packet_data += [payload.size].pack("c") # size byte
    packet_data += payload

    packet_data
  end

  def make_read_payload
    payload = [datastore['UNIT_NUMBER']].pack("c")
    payload += [@function_code].pack("c")
    payload += [datastore['DATA_ADDRESS']].pack("n")
    payload += [datastore['NUMBER']].pack("n")
    make_payload(payload)
  end

  def make_write_coil_payload(data)
    payload = [datastore['UNIT_NUMBER']].pack("c")
    payload += [@function_code].pack("c")
    payload += [datastore['DATA_ADDRESS']].pack("n")
    payload += [data].pack("c")
    payload += "\x00"

    packet_data = make_payload(payload)

    packet_data
  end

  def make_write_coils_payload(data, byte)
    payload = [datastore['UNIT_NUMBER']].pack("c")
    payload += [@function_code].pack("c")
    payload += [datastore['DATA_ADDRESS']].pack("n")
    payload += [datastore['DATA_COILS'].size].pack("n") # bit count
    payload += [byte].pack("c") # byte count
    for i in 0..(byte-1)
      payload += [data[i]].pack("b*")
    end

    packet_data = make_payload(payload)

    packet_data
  end

  def make_write_register_payload(data)
    payload = [datastore['UNIT_NUMBER']].pack("c")
    payload += [@function_code].pack("c")
    payload += [datastore['DATA_ADDRESS']].pack("n")
    payload += [data].pack("n")

    make_payload(payload)
  end

  def make_write_registers_payload(data, size)
    payload = [datastore['UNIT_NUMBER']].pack("c")
    payload += [@function_code].pack("c")
    payload += [datastore['DATA_ADDRESS']].pack("n")
    payload += [size].pack("n") # word count
    payload += [2*size].pack("c") # byte count
    for i in 0..(size-1)
      payload += [data[i]].pack("n")
    end

    make_payload(payload)
  end

  def handle_error(response)
    case response.reverse.unpack("c")[0].to_i
    when 1
      print_error("Error : ILLEGAL FUNCTION")
    when 2
      print_error("Error : ILLEGAL DATA ADDRESS")
    when 3
      print_error("Error : ILLEGAL DATA VALUE")
    when 4
      print_error("Error : SLAVE DEVICE FAILURE")
    when 6
      print_error("Error : SLAVE DEVICE BUSY")
    else
      print_error("Unknown error")
    end
    return
  end

  def read_coils
    if datastore['NUMBER']+datastore['DATA_ADDRESS'] > 65535
      print_error("Coils addresses go from 0 to 65535. You cannot go beyond.")
      return
    end
    @function_code = 0x1
    print_status("Sending READ COILS...")
    response = send_frame(make_read_payload)
    values = []
    if response.nil?
      print_error("No answer for the READ COILS")
      return
    elsif response.unpack("C*")[7] == (0x80 | @function_code)
      handle_error(response)
    elsif response.unpack("C*")[7] == @function_code
      loop = (datastore['NUMBER']-1)/8
      for i in 0..loop
        bin_value = response[9+i].unpack("b*")[0]
        list = bin_value.split("")
        for j in 0..7
          list[j] = list[j].to_i
          values[i*8 + j] = list[j]
        end
      end
      values = values[0..(datastore['NUMBER']-1)]
      print_good("#{datastore['NUMBER']} coil values from address #{datastore['DATA_ADDRESS']} : ")
      print_good("#{values}")
    else
      print_error("Unknown answer")
    end
  end

  def read_registers
    if datastore['NUMBER']+datastore['DATA_ADDRESS'] > 65535
      print_error("Registers addresses go from 0 to 65535. You cannot go beyond.")
      return
    end
    @function_code = 3
    print_status("Sending READ REGISTERS...")
    response = send_frame(make_read_payload)
    values = []
    if response.nil?
      print_error("No answer for the READ REGISTERS")
    elsif response.unpack("C*")[7] == (0x80 | @function_code)
      handle_error(response)
    elsif response.unpack("C*")[7] == @function_code
      for i in 0..(datastore['NUMBER']-1)
        values.push(response[9+2*i..10+2*i].unpack("n")[0])
      end
      print_good("#{datastore['NUMBER']} register values from address #{datastore['DATA_ADDRESS']} : ")
      print_good("#{values}")
    else
      print_error("Unknown answer")
    end
  end

  def write_coil
    @function_code = 5
    if datastore['DATA'] == 0
      data = 0
    elsif datastore['DATA'] == 1
      data = 255
    else
      print_error("Data value must be 0 or 1 in WRITE_COIL mode")
      return
    end
    print_status("Sending WRITE COIL...")
    response = send_frame(make_write_coil_payload(data))
    if response.nil?
      print_error("No answer for the WRITE COIL")
    elsif response.unpack("C*")[7] == (0x80 | @function_code)
      handle_error(response)
    elsif response.unpack("C*")[7] == @function_code
      print_good("Value #{datastore['DATA']} successfully written at coil address #{datastore['DATA_ADDRESS']}")
    else
      print_error("Unknown answer")
    end
  end

  def write_coils
    @function_code = 15
    temp = datastore['DATA_COILS']
    check = temp.split("")
    if temp.size > 65535
      print_error("DATA_COILS size must be between 0 and 65535")
      return
    end
    for j in check
      if j=="0" or j=="1"
      else
        print_error("DATA_COILS value must only contain 0s and 1s without space")
        return
      end
    end
    byte_number = (temp.size-1)/8 + 1
    data = []
    for i in 0..(byte_number-1)
      data.push(temp[(i*8+0)..(i*8+7)])
    end
    print_status("Sending WRITE COILS...")
    response = send_frame(make_write_coils_payload(data, byte_number))
    if response.nil?
      print_error("No answer for the WRITE COILS")
    elsif response.unpack("C*")[7] == (0x80 | @function_code)
      handle_error(response)
    elsif response.unpack("C*")[7] == @function_code
      print_good("Values #{datastore['DATA_COILS']} successfully written from coil address #{datastore['DATA_ADDRESS']}")
    else
      print_error("Unknown answer")
    end
  end

  def write_register
    @function_code = 6
    if datastore['DATA'] < 0 || datastore['DATA'] > 65535
      print_error("Data to write must be an integer between 0 and 65535 in WRITE_REGISTER mode")
      return
    end
    print_status("Sending WRITE REGISTER...")
    response = send_frame(make_write_register_payload(datastore['DATA']))
    if response.nil?
      print_error("No answer for the WRITE REGISTER")
    elsif response.unpack("C*")[7] == (0x80 | @function_code)
      handle_error(response)
    elsif response.unpack("C*")[7] == @function_code
      print_good("Value #{datastore['DATA']} successfully written at registry address #{datastore['DATA_ADDRESS']}")
    else
      print_error("Unknown answer")
    end
  end

  def write_registers
    @function_code = 16
    check = datastore['DATA_REGISTERS'].split("")
    for j in 0..(check.size-1)
      if check[j] == "0" or check[j]== "1" or check[j]== "2" or check[j]== "3" or check[j]== "4" or check[j]== "5" or check[j]== "6" or check[j]== "7" or check[j]== "8" or check[j]== "9" or check[j]== ","
        if check[j] == "," and check[j+1] == ","
          print_error("DATA_REGISTERS cannot contain two consecutive commas")
          return
        end
      else
        print_error("DATA_REGISTERS value must only contain numbers and commas without space")
        return
      end
    end
    list = datastore['DATA_REGISTERS'].split(",")
    if list.size+datastore['DATA_ADDRESS'] > 65535
      print_error("Registers addresses go from 0 to 65535. You cannot go beyond.")
      return
    end
    data = []
    for i in 0..(list.size-1)
      data[i] = list[i].to_i
    end
    for j in 0..(data.size-1)
      if data[j] < 0 || data[j] > 65535
        print_error("Each word to write must be an integer between 0 and 65535 in WRITE_REGISTERS mode")
        return
      end
    end
    print_status("Sending WRITE REGISTERS...")
    response = send_frame(make_write_registers_payload(data, data.size))
    if response.nil?
      print_error("No answer for the WRITE REGISTERS")
    elsif response.unpack("C*")[7] == (0x80 | @function_code)
      handle_error(response)
    elsif response.unpack("C*")[7] == @function_code
      print_good("Values #{datastore['DATA_REGISTERS']} successfully written from registry address #{datastore['DATA_ADDRESS']}")
    else
      print_error("Unknown answer")
    end
  end

  def run
    @modbus_counter = 0x0000 # used for modbus frames
    connect
    case action.name
    when "READ_COILS"
      read_coils
    when "READ_REGISTERS"
      read_registers
    when "WRITE_COIL"
      write_coil
    when "WRITE_REGISTER"
      write_register
    when "WRITE_COILS"
      if datastore['DATA_COILS'] == nil
        print_error("The following option is needed in WRITE_COILS mode: DATA_COILS.")
        return
      else
        write_coils
      end
    when "WRITE_REGISTERS"
      if datastore['DATA_REGISTERS'] == nil
        print_error("The following option is needed in WRITE_REGISTERS mode: DATA_REGISTERS.")
        return
      else
        write_registers
      end
    else
      print_error("Invalid ACTION")
    end
    disconnect
  end
end