metasploit-framework/lib/rex/proto/rfb/client.rb

# -*- coding: binary -*-

##
#
# RFB protocol support
#
# by Joshua J. Drake <jduck>
#
# Based on:
# vnc_auth_none contributed by Matteo Cantoni <goony[at]nothink.org>
# vnc_auth_login contributed by carstein <carstein.sec[at]gmail.com>
#
# TODO: determine how to detect a view-only session.
##

module Rex
module Proto
module RFB

class Client

  def initialize(sock, opts = {})
    @sock = sock
    @opts = opts

    @banner = nil
    @majver = MajorVersions
    @minver = -1
    @auth_types = []
  end

  def read_error_message
    len = @sock.get_once(4)
    return 'Unknown error' if not len or len.length != 4

    len = len.unpack("N").first
    @sock.get_once(len)
  end

  def handshake
    @banner = @sock.get_once(12)
    if not @banner
      @error = "Unable to obtain banner from server"
      return false
    end

    # RFB Protocol Version 3.3 (1998-01)
    # RFB Protocol Version 3.7 (2003-08)
    # RFB Protocol Version 3.8 (2007-06)

    if @banner =~ /RFB ([0-9]{3})\.([0-9]{3})/
      maj = $1.to_i
      unless MajorVersions.include?(maj)
        @error = "Invalid major version number: #{maj}"
        return false
      end
    else
      @error = "Invalid RFB banner: #{@banner}"
      return false
    end

    @minver = $2.to_i

    # Forces version 3 to be used. This adds support  for version 4 servers.
    # It may be necessary to hardcode minver as well.
    # TODO: Add support for Version 4.
    # Version 4 adds additional information to the packet regarding supported
    # authentication types.
    our_ver = "RFB %03d.%03d\n" % [3, @minver]
    @sock.put(our_ver)

    true
  end

  def connect(password = nil)
    return false if not handshake
    return false if not authenticate(password)
    return false if not send_client_init
    true
  end

  def send_client_init
    if @opts[:exclusive]
      @sock.put("\x00") # do share.
    else
      @sock.put("\x01") # do share.
    end
  end

  def authenticate(password = nil)
    type = negotiate_authentication
    return false if not type

    # Authenticate.
    case type
    when AuthType::None
      # Nothing here.

    when AuthType::VNC
      return false if not negotiate_vnc_auth(password)

    end

    # Handle reading the security result message
    result = @sock.get_once(4)
    if not result
      @error = "Unable to read auth result"
      return false
    end

    result = result.unpack('N').first
    case result
    when 0
      return true

    when 1
      if @minver >= 8
        msg = read_error_message
        @error = "Authentication failed: #{msg}"
      else
        @error = "Authentication failed"
      end
    when 2
      @error = "Too many authentication attempts"
    else
      @error = "Unknown authentication result: #{result}"
    end

    false
  end

  def negotiate_authentication
    # Authentication type negotiation is protocol version specific.
    if @minver < 7
      buf = @sock.get_once(4)
      if not buf
        @error = "Unable to obtain requested authentication method"
        return nil
      end
      @auth_types = buf.unpack('N')
      if not @auth_types or @auth_types.first == 0
        msg = read_error_message
        @error = "No authentication types available: #{msg}"
        return nil
      end
    else
      buf = @sock.get_once(1)
      if not buf
        @error = "Unable to obtain supported authentication method count"
        return nil
      end

      # first byte is number of security types
      num_types = buf.unpack("C").first
      if (num_types == 0)
        msg = read_error_message
        @error = "No authentication types available: #{msg}"
        return nil
      end

      buf = @sock.get_once(num_types)
      if not buf or buf.length != num_types
        @error = "Unable to read authentication types"
        return nil
      end

      @auth_types = buf.unpack("C*")
    end

    if not @auth_types or @auth_types.length < 1
      @error = "No authentication types found"
      return nil
    end

    # Select the one we prefer
    selected = nil
    selected ||= AuthType::None if @opts[:allow_none] and @auth_types.include? AuthType::None
    selected ||= AuthType::VNC if @auth_types.include? AuthType::VNC

    if not selected
      @error = "No supported authentication method found."
      return nil
    end

    # For 3.7 and later, clients must state which security-type to use
    @sock.put([selected].pack('C')) if @minver >= 7

    selected
  end

  def negotiate_vnc_auth(password = nil)
    challenge = @sock.get_once(16)
    if not challenge or challenge.length != 16
      @error = "Unable to obtain VNC challenge"
      return false
    end

    response = Cipher.encrypt(challenge, password)
    @sock.put(response)

    true
  end

  attr_reader :error, :majver, :minver, :auth_types
  attr_reader :view_only
end

end
end
end