local bin = require "bin" local coroutine = require "coroutine" local dhcp = require "dhcp" local ipOps = require "ipOps" local math = require "math" local nmap = require "nmap" local packet = require "packet" local stdnse = require "stdnse" local string = require "string" local table = require "table" description = [[ Sends a DHCP request to the broadcast address (255.255.255.255) and reports the results. The script uses a static MAC address (DE:AD:CO:DE:CA:FE) while doing so in order to prevent scope exhaustion. The script reads the response using pcap by opening a listening pcap socket on all available ethernet interfaces that are reported up. If no response has been received before the timeout has been reached (default 10 seconds) the script will abort execution. The script needs to be run as a privileged user, typically root. ]] --- -- @usage -- sudo nmap --script broadcast-dhcp-discover -- -- @output -- | broadcast-dhcp-discover: -- | IP Offered: 192.168.1.114 -- | DHCP Message Type: DHCPOFFER -- | Server Identifier: 192.168.1.1 -- | IP Address Lease Time: 1 day, 0:00:00 -- | Subnet Mask: 255.255.255.0 -- | Router: 192.168.1.1 -- | Domain Name Server: 192.168.1.1 -- |_ Domain Name: localdomain -- -- @args broadcast-dhcp-discover.timeout time in seconds to wait for a response -- (default: 10s) -- -- Version 0.1 -- Created 07/14/2011 - v0.1 - created by Patrik Karlsson 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 if nmap.address_family() ~= 'inet' then stdnse.print_debug("%s is IPv4 compatible only.", SCRIPT_NAME) return false end return true end -- Creates a random MAC address -- -- @return mac_addr string containing a random MAC local function randomizeMAC() local mac_addr = "" for j=1, 6 do mac_addr = mac_addr .. string.char(math.random(1, 255)) end return mac_addr end -- Gets a list of available interfaces based on link and up filters -- -- @param link string containing the link type to filter -- @param up string containing the interface status to filter -- @return result table containing the matching interfaces local function getInterfaces(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 ) then result = result or {} result[iface.device] = true end end end return result end -- Listens for an incoming dhcp response -- -- @param iface string with the name of the interface to listen to -- @param timeout number of ms to wait for a response -- @param xid the DHCP transaction id -- @param result a table to which the result is written local function dhcp_listener(sock, timeout, xid, result) local condvar = nmap.condvar(result) sock:set_timeout(100) local start_time = nmap.clock_ms() while( nmap.clock_ms() - start_time < timeout ) do local status, _, _, data = sock:pcap_receive() -- abort, once another thread has picked up our response if ( #result > 0 ) then sock:close() condvar "signal" return end if ( status ) then local p = packet.Packet:new( data, #data ) if ( p and p.udp_dport ) then local data = data:sub(p.udp_offset + 9) local status, response = dhcp.dhcp_parse(data, xid) if ( status ) then table.insert( result, response ) sock:close() condvar "signal" return end end end end sock:close() condvar "signal" end action = function() local host, port = "255.255.255.255", 67 local timeout = stdnse.get_script_args("broadcast-dhcp-discover.timeout") timeout = tonumber(timeout) or 10 -- convert from seconds to ms timeout = timeout * 1000 -- randomizing the MAC could exhaust dhcp servers with small scopes -- if ran multiple times, so we should probably refrain from doing -- this? local mac = string.char(0xDE,0xAD,0xC0,0xDE,0xCA,0xFE)--randomizeMAC() local interfaces -- first check if the user supplied an interface if ( nmap.get_interface() ) then interfaces = { [nmap.get_interface()] = true } else -- As the response will be sent to the "offered" ip address we need -- to use pcap to pick it up. However, we don't know what interface -- our packet went out on, so lets get a list of all interfaces and -- run pcap on all of them, if they're a) up and b) ethernet. interfaces = getInterfaces("ethernet", "up") end if( not(interfaces) ) then return "\n ERROR: Failed to retrieve interfaces (try setting one explicitly using -e)" end local transaction_id = bin.pack("I", ipOps.todword("0.0.0.0")) -- we nead to set the flags to broadcast local request_options, overrides, lease_time = nil, { flags = 0x8000 }, nil local status, packet = dhcp.dhcp_build(request_type, ip_address, mac, nil, request_options, overrides, lease_time, transaction_id) if (not(status)) then return "\n ERROR: Failed to build packet" end local threads = {} local result = {} local condvar = nmap.condvar(result) -- start a listening thread for each interface for iface, _ in pairs(interfaces) do local sock, co sock = nmap.new_socket() sock:pcap_open(iface, 1500, false, "ip && udp && port 68") co = stdnse.new_thread( dhcp_listener, sock, timeout, transaction_id, result ) threads[co] = true end local socket = nmap.new_socket("udp") socket:bind(nil, 68) socket:sendto( host, port, packet ) socket:close() -- wait until all threads are done repeat condvar "wait" for thread in pairs(threads) do if coroutine.status(thread) == "dead" then threads[thread] = nil end end until next(threads) == nil local response = {} -- Display the results for i, r in ipairs(result) do table.insert(response, string.format("IP Offered: %s", r.yiaddr_str)) for _, v in ipairs(r.options) do if(type(v['value']) == 'table') then table.insert(response, string.format("%s: %s", v['name'], stdnse.strjoin(", ", v['value']))) else table.insert(response, string.format("%s: %s\n", v['name'], v['value'])) end end end return stdnse.format_output(true, response) end