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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Auxiliary
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  include Msf::Auxiliary::Scanner
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  include Msf::Exploit::Capture
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  def initialize
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    super(
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      'Name'         => 'BNAT Scanner',
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      'Description'  => %q{
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          This module is a scanner which can detect Broken NAT (network address translation)
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        implementations, which could result in an inability to reach ports on remote
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        machines. Typically, these ports will appear in nmap scans as 'filtered'/'closed'.
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        },
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      'Author'       =>
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        [
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          'bannedit',
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          'Jonathan Claudius <jclaudius[at]trustwave.com>',
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        ],
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      'License'      => MSF_LICENSE,
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      'References'   =>
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        [
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          [ 'URL', 'https://github.com/claudijd/bnat'],
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          [ 'URL', 'http://www.slideshare.net/claudijd/dc-skytalk-bnat-hijacking-repairing-broken-communication-channels']
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        ]
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    )
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    register_options(
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        [
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          OptString.new('PORTS', [true, "Ports to scan (e.g. 22-25,80,110-900)", "21,22,23,80,443"]),
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          OptString.new('INTERFACE', [true, "The name of the interface", "eth0"]),
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          OptInt.new('TIMEOUT', [true, "The reply read timeout in milliseconds", 500])
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        ])
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    deregister_options('FILTER','PCAPFILE','SNAPLEN')
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  end
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  def probe_reply(pcap, to)
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    reply = nil
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    begin
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      Timeout.timeout(to) do
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        pcap.each do |r|
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          pkt = PacketFu::Packet.parse(r)
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          next unless pkt.is_tcp?
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          reply = pkt
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          break
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        end
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      end
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      rescue Timeout::Error
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    end
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    return reply
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  end
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  def generate_probe(ip)
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    ftypes = %w{windows, linux, freebsd}
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    @flavor = ftypes[rand(ftypes.length)]
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    config = PacketFu::Utils.whoami?(:iface => datastore['INTERFACE'])
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    p = PacketFu::TCPPacket.new(:config => config)
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    p.ip_daddr = ip
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    p.tcp_flags.syn = 1
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    return p
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  end
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  def run_host(ip)
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    open_pcap
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    to = (datastore['TIMEOUT'] || 500).to_f / 1000.0
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    p = generate_probe(ip)
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    pcap = self.capture
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    ports = Rex::Socket.portspec_crack(datastore['PORTS'])
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    if ports.empty?
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      raise Msf::OptionValidateError.new(['PORTS'])
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    end
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    ports.each_with_index do |port,i|
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      p.tcp_dst = port
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      p.tcp_src = rand(64511)+1024
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      p.tcp_seq = rand(64511)+1024
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      p.recalc
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      ackbpf = "tcp [8:4] == 0x#{(p.tcp_seq + 1).to_s(16)}"
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      pcap.setfilter("tcp and tcp[13] == 18 and not host #{ip} and src port #{p.tcp_dst} and dst port #{p.tcp_src} and #{ackbpf}")
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      break unless capture_sendto(p, ip)
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      reply = probe_reply(pcap, to)
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      next if reply.nil?
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      print_status("[BNAT RESPONSE] Requested IP: #{ip} Responding IP: #{reply.ip_saddr} Port: #{reply.tcp_src}")
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    end
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    close_pcap
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  end
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end
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