id = "PPTP"
description = [[
Attempts to extract system information from the PPTP service.
]]
-- rev 0.2 (11-14-2007)

author = "Thomas Buchanan <tbuchanan@thecompassgrp.net>"

license = "Same as Nmap--See http://nmap.org/book/man-legal.html"

categories = {"version"}

require "comm"
require "shortport"

portrule = shortport.portnumber(1723)

action = function(host, port)
	local payload
	  
	-- build a PPTP Start-Control-Connection-Request packet
	-- copied from packet capture of pptp exchange
	-- for details of packet structure, see http://www.ietf.org/rfc/rfc2637.txt
	payload = "\000\156\000\001\026\043\060\077" -- length=156, Message type=control, cookie
	payload = payload .. "\000\001\000\000\001\000\000\000" -- Control type=Start-Control-Connection-Request, Reserved, Protocol=1.0, Reserverd
	payload = payload .. "\000\000\000\001\000\000\000\001" -- Framing Capabilities, Bearer Capabilities
	payload = payload .. "\255\255\000\001" .. "none" -- Maximum channels, firmware version, hostname
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for hostname
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for hostname
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for hostname
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for hostname
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for hostname
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for hostname
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for hostname
	payload = payload .. "\000\000\000\000" .. "nmap" -- padding for hostname, vendor name
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for vendor name
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for vendor name
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for vendor name
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for vendor name
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for vendor name
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for vendor name
	payload = payload .. "\000\000\000\000\000\000\000\000" -- padding for vendor name
	payload = payload .. "\000\000\000\000" -- padding for vendor name

	local try = nmap.new_try()
	local response = try(comm.exchange(host, port, payload, {timeout=5000}))

	local result
		
	-- check to see if the packet we got back matches the beginning of a PPTP Start-Control-Connection-Reply packet
	result = string.match(response, "%z\156%z\001\026\043(.*)")
	local output
	
	if result ~= nil then
		local firmware
		local hostname
		local vendor
		
		-- get the firmware version (2 octets) 
		local s1,s2
		s1,s2 = string.byte(result, 22, 23)
		firmware = s1 * 256 + s2

		-- get the hostname (64 octets)
		local s3
		s3 = string.sub(result, 24, 87)
		hostname = string.match(s3, "(.-)%z")

		-- get the vendor (should be 64 octets, but capture to end of the string to be safe)
		local s4, length
		length = string.len(result)
		s4 = string.sub(result, 88, length)
		vendor = string.match(s4, "(.-)%z")
	
		port.version.name = "pptp"
		port.version.name_confidence = 10
		if vendor ~= nil then port.version.product = vendor end
		if firmware ~= 0 then port.version.version = "(Firmware: " .. firmware .. ")" end
		if hostname ~= nil then port.version.hostname = hostname end
		
		port.version.service_tunnel = "none"
		port.version.fingerprint = nil
		nmap.set_port_version(host, port, "hardmatched")
	end

end
