broadcast-listener.nse

local _G = require "_G"
local bin = require "bin"
local coroutine = require "coroutine"
local nmap = require "nmap"
local packet = require "packet"
local stdnse = require "stdnse"
local table = require "table"

description = [[ 
Sniffs the network for incoming broadcast communication and
attempts to decode the received packets. It supports protocols like CDP, HSRP,
Spotify, DropBox, DHCP, ARP and a few more. See packetdecoders.lua for more
information.

The script attempts to sniff all ethernet based interfaces with an IPv4 address
unless a specific interface was given using the -e argument to Nmap.
]]

---
-- @usage
-- nmap --script broadcast-listener
-- nmap --script broadcast-listener -e eth0
--
-- @output
-- | broadcast-listener: 
-- |   udp
-- |       Netbios
-- |         ip           query
-- |         192.168.0.60 \x01\x02__MSBROWSE__\x02\x01
-- |       DHCP
-- |         srv ip       cli ip       mask             gw           dns
-- |         192.168.0.1  192.168.0.5  255.255.255.0    192.168.0.1  192.168.0.18, 192.168.0.19
-- |       DropBox
-- |         displayname  ip            port   version  host_int  namespaces
-- |         39000860     192.168.0.107 17500  1.8      39000860  28814673, 29981099
-- |       HSRP
-- |         ip             version  op     state   prio  group  secret  virtual ip
-- |         192.168.0.254  0        Hello  Active  110   1      cisco   192.168.0.253
-- |   ether
-- |       CDP
-- |         ip  id      platform       version
-- |         ?   Router  cisco 7206VXR  12.3(23)
-- |       ARP Request
-- |         sender ip     sender mac         target ip
-- |         192.168.0.101 00:04:30:26:DA:C8  192.168.0.60
-- |_        192.168.0.1   90:24:1D:C8:B9:AE  192.168.0.60
--
-- @args broadcast-listener.timeout specifies the amount of seconds to sniff
--       the network interface. (default 30s)
--
-- The script attempts to discover all available ipv4 network interfaces,
-- unless the Nmap -e argument has been supplied, and then starts sniffing
-- packets on all of the discovered interfaces. It sets a BPF filter to exclude
-- all packets that have the interface address as source or destination in
-- order to capture broadcast traffic.
--
-- Incoming packets can either be either layer 3 (usually UDP) or layer 2.
-- Depending on the layer the packet is matched against a packet decoder loaded
-- from the external nselib/data/packetdecoder.lua file. A more detailed
-- description on how the decoders work can be found in that file.
-- In short, there are two different types of decoders: udp and ether.
-- The udp decoders get triggered by the destination port number, while the
-- ether decoders are triggered by a pattern match. The port or pattern is used
-- as an index in a table containing functions to process packets and fetch
-- the decoded results.
-- 


--
-- Version 0.1
-- Created 07/02/2011 - v0.1 - created by Patrik Karlsson <patrik@cqure.net>
-- Revised 07/25/2011 - v0.2 -  
--								* added more documentation
--								* added getInterfaces code to detect available
--								  interfaces.
--								* corrected bug that would fail to load
--								  decoders if not in a relative directory.



author = "Patrik Karlsson"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"broadcast", "safe"}




prerule = function()
	if not nmap.is_privileged() then
		stdnse.print_verbose("%s not running for lack of privileges.", SCRIPT_NAME)
		return false
	end
	return true
end

---
-- loads the decoders from file
--
-- @param fname string containing the name of the file
-- @return status true on success false on failure
-- @return decoders table of decoder functions on success
-- @return err string containing the error message on failure
loadDecoders = function(fname)
	-- resolve the full, absolute, path
	local abs_fname = nmap.fetchfile(fname)

	if ( not(abs_fname) ) then
		return false, ("ERROR: Failed to load decoder definition (%s)"):format(fname)
	end

	local env = setmetatable({Decoders = {}}, {__index = _G});
	local file = loadfile(abs_fname, "t", env)
	if(not(file)) then
		stdnse.print_debug("%s: Couldn't load decoder file: %s", SCRIPT_NAME, fname)
		return false, "ERROR: Couldn't load decoder file: " .. fname
	end
	
	file()

	local d = env.Decoders

	if ( d ) then return true, d end
	return false, "ERROR: Failed to load decoders"
end

---
-- Starts sniffing the selected interface for packets with a destination that
-- is not explicitly ours (broadcast, multicast etc.)
-- 
-- @param iface table containing <code>name</code> and <code>address</code>
-- @param Decoders the decoders class loaded externally
-- @param decodertab the "result" table to which all discovered items are
--			reported
sniffInterface = function(iface, Decoders, decodertab)
	local condvar = nmap.condvar(decodertab)
	local sock = nmap.new_socket()
	local timeout = tonumber(stdnse.get_script_args("broadcast-listener.timeout"))

	-- default to 30 seconds, if nothing else was set
	timeout = timeout and (timeout * 1000) or (30 * 1000)

	-- We want all packets that aren't explicitly for us
 	sock:pcap_open(iface.name, 1500, true, ("!host %s"):format(iface.address))

	-- Set a short timeout so that we can timeout in time if needed
	sock:set_timeout(100)

	local start_time = nmap.clock_ms()
	while( nmap.clock_ms() - start_time < timeout ) do
		local status, _, _, data = sock:pcap_receive()
	
		if ( status ) then
			local p = packet.Packet:new( data, #data )

			-- if we have an UDP-based broadcast, we should have a proper packet
			if ( p and p.udp_dport and ( decodertab.udp[p.udp_dport] or Decoders.udp[p.udp_dport] ) ) then
				if ( not(decodertab.udp[p.udp_dport]) ) then
					decodertab.udp[p.udp_dport] = Decoders.udp[p.udp_dport]:new()
				end
				decodertab.udp[p.udp_dport]:process(data)
			-- The packet was decoded successfully but we don't have a valid decoder
			-- Report this
			elseif ( p and p.udp_dport ) then
				stdnse.print_debug(2, "No decoder for dst port %d", p.udp_dport)
			-- we don't have a packet, so this is most likely something layer2 based
			-- in that case, check the ether Decoder table for pattern matches
			else
				-- attempt to find a match for a pattern
				local pos, hex = bin.unpack("H" .. #data, data)
				local decoded = false
				for match, _ in pairs(Decoders.ether) do
					-- attempts to match the "raw" packet against a filter
					-- supplied in each ethernet packet decoder
					if ( hex:match(match) ) then
						if ( not(decodertab.ether[match]) ) then
							decodertab.ether[match] = Decoders.ether[match]:new()
						end
						-- start a new decoding thread. This way, if something gets foobared
						-- the whole script doesn't break, only the packet decoding for that
						-- specific packet.
						stdnse.new_thread( decodertab.ether[match].process, decodertab.ether[match], data )
						decoded = true
					end
				end
				-- no decoder was found for this layer2 packet
				if ( not(decoded) and #data > 10 ) then
					stdnse.print_debug(2, "No decoder for packet hex: %s", select(2, bin.unpack("H10", data) ) )
				end
			end
		end
	end
	condvar "signal"
end

---
-- Gets a list of available interfaces based on link and up filters
-- Interfaces are only added if they've got an ipv4 address 
--
-- @param link string containing the link type to filter
-- @param up string containing the interface status to filter
-- @return result table containing tables of interfaces
--			each interface table has the following fields:
--			<code>name</code> containing the device name
--			<code>address</code> containing the device address
getInterfaces = function(link, up)
	if( not(nmap.list_interfaces) ) then return end
	local interfaces, err = nmap.list_interfaces()
	local result = {}
	if ( not(err) ) then
		for _, iface in ipairs(interfaces) do
			if ( iface.link == link and 
				 iface.up == up and
				 iface.address ) then 
				
				-- exclude ipv6 addresses for now
				if ( not(iface.address:match(":")) ) then
					table.insert(result, { name = iface.device, 
										address = iface.address } )
				end
			end
		end
	end
	return result
end

action = function()

	local DECODERFILE = "nselib/data/packetdecoders.lua"
	local iface = nmap.get_interface()
	local interfaces = {}
	
	-- was an interface supplied using the -e argument?
	if ( iface ) then	
		local iinfo, err = nmap.get_interface_info(iface)
	
		if ( not(iinfo.address) ) then
			return "\n  ERROR: The IP address of the interface could not be determined ..."
		end
		
		interfaces = { { name = iface, address = iinfo.address } }
	else
		-- no interface was supplied, attempt autodiscovery
		interfaces = getInterfaces("ethernet", "up")
	end
	
	-- make sure we have at least one interface to start sniffing
	if ( #interfaces == 0 ) then
		return "\n  ERROR: Could not determine any valid interfaces"
	end

	-- load the decoders from file
	local status, Decoders = loadDecoders(DECODERFILE)
	if ( not(status) ) then return "\n  " .. Decoders end
	
	-- create a local table to handle instantiated decoders
	local decodertab = { udp = {}, ether = {} }
	local condvar = nmap.condvar(decodertab)
	local threads = {}
	
	-- start a thread for each interface to sniff
	for _, iface in ipairs(interfaces) do
		local co = stdnse.new_thread(sniffInterface, iface, Decoders, decodertab)
		threads[co] = true
	end
	
	-- wait for all threads to finish sniffing
    repeat
		for thread in pairs(threads) do
			if coroutine.status(thread) == "dead" then
				threads[thread] = nil
			end
		end
		if ( next(threads) ) then
			condvar "wait"
		end
	until next(threads) == nil

	local out_outer = {}
	
	-- create the results table
	for proto, _ in pairs(decodertab) do
		local out_inner = {}
		for key, decoder in pairs(decodertab[proto]) do
			table.insert( out_inner, decodertab[proto][key]:getResults() )
		end
		if ( #out_inner > 0 ) then
			table.insert( out_outer, { name = proto, out_inner } )
		end
	end
	
	return stdnse.format_output(true, out_outer)

end