Class: BetterCap::Network::Servers::DNSD

Inherits:
Object
  • Object
show all
Defined in:
lib/bettercap/network/servers/dnsd.rb

Overview

Simple DNS server class used for DNS spoofing.

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(hosts_filename = nil, address = '0.0.0.0', port = 5300) ⇒ DNSD

Initialize the DNS server with the specified address and tcp/udp port. The server will load hosts_filename composed by ‘regexp -> ip’ entries to do custom DNS spoofing/resolution.



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# File 'lib/bettercap/network/servers/dnsd.rb', line 48

def initialize( hosts_filename = nil, address = '0.0.0.0', port = 5300 )
  @port    = port
  @address = address
  @hosts   = hosts_filename
  @server  = nil
  @ifaces  = [
    [:udp, address, port],
    [:tcp, address, port]
  ]
end

Class Method Details

.parse_hosts(filename) ⇒ Object

Parse hosts from filename, example host file:

# *.google.com will point to the attacker’s computer. local .*google.com

# a custom redirection 12.12.12.12 wtf.idontexist.com

Raises:



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# File 'lib/bettercap/network/servers/dnsd.rb', line 114

def self.parse_hosts( filename )
  raise BetterCap::Error, "File '#{filename}' does not exist." unless File.exist?(filename)

  hosts = {}
  File.open(filename).each_with_index do |line,lineno|
    line = line.strip
    # skip empty lines and comments
    next if line.empty? or line[0] == '#'
    if line =~ /^([^\s]+)\s+(.+)$/
      address    = $1
      expression = $2

      if address == 'local'
        address = Context.get.iface.ip.to_s
      end

      raise BetterCap::Error, "Invalid IPv4 address '#{address}' on line #{lineno + 1} of '#{filename}'." \
        unless Network::Validator.is_ip?(address)

      begin
        hosts[ expression ] = address
      rescue RegexpError
        raise BetterCap::Error, "Invalid expression '#{expression}' on line #{lineno + 1} of '#{filename}'."
      end
    end
  end

  hosts
end

Instance Method Details

#add_rule!(exp, addr) ⇒ Object

Add a rule to the DNS resolver at runtime.



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# File 'lib/bettercap/network/servers/dnsd.rb', line 60

def add_rule!( exp, addr )
  Logger.debug "[#{'DNS'.green}] Adding rule: '#{exp}' -> '#{addr}' ..."

  block = Proc.new do |transaction|
    Logger.info "[#{transaction.options[:peer]} > #{'DNS'.green}] Received request for '#{transaction.question.to_s.yellow}', sending spoofed reply #{addr.yellow} ..."
    transaction.respond!(addr)
  end

  DnsWrapper.get.rules << RubyDNS::RuleBasedServer::Rule.new( [ Regexp.new(exp), Resolv::DNS::Resource::IN::A ], block )
end

#start ⇒ Object

Start the server.



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# File 'lib/bettercap/network/servers/dnsd.rb', line 72

def start
  Logger.info "[#{'DNS'.green}] Starting on #{@address}:#{@port} ..."

  options = {
    :listen => @ifaces,
    :asynchronous => true,
    :server_class => DnsWrapper
  }

  begin
    RubyDNS::run_server( options ) do
      # Suppress RubyDNS logging.
      @logger.level = ::Logger::ERROR
      @upstream ||= RubyDNS::Resolver.new([[:udp, "8.8.8.8", 53], [:tcp, "8.8.8.8", 53]])

      # Default DNS handler
      otherwise do |transaction|
        Logger.debug "[#{transaction.options[:peer]} > #{'DNS'.green}] Received request for '#{transaction.question.to_s.yellow}' -> upstream DNS"
        transaction.passthrough!(@upstream)
      end
    end

    unless @hosts.nil?
      DNSD.parse_hosts( @hosts ).each do |exp,addr|
        add_rule!( exp, addr )
      end
    end
  rescue Errno::EADDRINUSE
    raise BetterCap::Error, "[DNS] It looks like there's another process listening on #{@address}:#{@port}, please chose a different port."
  end
end

#stop ⇒ Object

Stop the server.



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# File 'lib/bettercap/network/servers/dnsd.rb', line 105

def stop; end