##
# $Id$
##

##
# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# web site for more information on licensing and terms of use.
#   http://metasploit.com/
##

require 'msf/core'
require 'timeout'

class Metasploit3 < Msf::Auxiliary

	include Msf::Exploit::Capture
	include Msf::Auxiliary::Scanner
	include Msf::Auxiliary::Report

	def initialize
		super(
			'Name'        => 'IPID Sequence Scanner',
			'Description' => %q{
				This module will probe hosts' IPID sequences and classify
				them using the same method Nmap uses when it's performing
				its IPID Idle Scan (-sI) and OS Detection (-O).

				Nmap's probes are SYN/ACKs while this module's are SYNs.
				While this does not change the underlying functionality,
				it does change the chance of whether or not the probe
				will be stopped by a firewall.

				Nmap's Idle Scan can use hosts whose IPID sequences are
				classified as "Incremental" or "Broken little-endian incremental".
			},
			'Author'      => 'kris katterjohn',
			'License'     => MSF_LICENSE,
			'Version'     => '$Revision$'
		)

		register_options([
			Opt::RPORT(80),
			OptInt.new('TIMEOUT', [true, "The reply read timeout in milliseconds", 500]),
			OptString.new('INTERFACE', [false, 'The name of the interface'])
		])

		register_advanced_options([
			OptInt.new('SAMPLES', [true, "The IPID sample size", 6])
		])

		deregister_options('FILTER','PCAPFILE')
	end

	def rport
		datastore['RPORT'].to_i
	end

	def run_host(ip)
		open_pcap

		raise "SAMPLES option must be >= 2" if datastore['SAMPLES'] < 2

		pcap = self.capture

		shost = Rex::Socket.source_address(ip)

		to = (datastore['TIMEOUT'] || 500).to_f / 1000.0

		ipids = []

		pcap.setfilter(getfilter(shost, ip, rport))

		datastore['SAMPLES'].times do
			sport = rand(0xffff - 1025) + 1025

			probe = buildprobe(shost, sport, ip, rport)

			capture_sendto(probe, ip)

			reply = probereply(pcap, to)

			next if not reply

			ipids << reply.ip_id
		end

		close_pcap

		return if ipids.empty?

		print_status("#{ip}'s IPID sequence class: #{analyze(ipids)}")

		#Add Report
		report_note(
			:host	=> ip,
			:proto	=> 'ip',
			:type	=> 'IPID sequence',
			:data	=> "IPID sequence class: #{analyze(ipids)}"
		)
	end

	# Based on Nmap's get_ipid_sequence() in osscan2.cc
	def analyze(ipids)
		allzeros = true
		allsame = true
		mul256 = true
		inc = true

		# ipids.each do |ipid|
		#	print_status("Got IPID ##{ipid}")
		# end

		return "Unknown" if ipids.size < 2

		diffs = []
		i = 1

		while i < ipids.size
			p = ipids[i - 1]
			c = ipids[i]

			if p != 0 or c != 0
				allzeros = false
			end

			if p <= c
				diffs[i - 1] = c - p
			else
				diffs[i - 1] = c - p + 65536
			end

			if ipids.size > 2 and diffs[i - 1] > 20000
				return "Randomized"
			end

			i += 1
		end

		return "All zeros" if allzeros

		diffs.each do |diff|
			if diff > 1000 and ((diff % 256) != 0 or ((diff % 256) == 0 and diff >= 25600))
				return "Random positive increments"
			end

			allsame = false if diff != 0

			mul256 = false if diff > 5120 or (diff % 256) != 0

			inc = false if diff >= 10
		end

		return "Constant" if allsame

		return "Broken little-endian incremental!" if mul256

		return "Incremental!" if inc

		"Unknown"
	end

	def getfilter(shost, dhost, dport)
		"tcp and src host #{dhost} and src port #{dport} and " +
		"dst host #{shost}"
	end

	# This gets set via the usual capture_sendto interface
	def buildprobe(shost, sport, dhost, dport)
		p = PacketFu::TCPPacket.new
		p.ip_saddr = shost
		p.ip_daddr = dhost
		p.tcp_sport = sport
		p.tcp_dport = dport
		p.tcp_flags.syn = 1
		p.recalc
		p
	end

	def probereply(pcap, to)
		reply = nil

		begin
			Timeout.timeout(to) do
				pcap.each do |r|
					pkt = PacketFu::Packet.parse(r)
					next unless pkt.is_tcp?
					next unless pkt.tcp_flags.syn == 1 || pkt.tcp_flags.rst == 1
					reply = pkt
					break
				end
			end
		rescue Timeout::Error
		end

		return reply
	end

end
