local dhcp = require "dhcp" local math = require "math" local nmap = require "nmap" local shortport = require "shortport" local stdnse = require "stdnse" local string = require "string" local table = require "table" description = [[ Sends a DHCPINFORM request to a host on UDP port 67 to obtain all the local configuration parameters without allocating a new address. DHCPINFORM is a DHCP request that returns useful information from a DHCP server, without allocating an IP address. The request sends a list of which fields it wants to know (a handful by default, every field if verbosity is turned on), and the server responds with the fields that were requested. It should be noted that the server doesn't have to return every field, nor does it have to return them in the same order, or honour the request at all. A Linksys WRT54g, for example, completely ignores the list of requested fields and returns a few standard ones. This script displays every field it receives. With script arguments, the type of DHCP request can be changed, which can lead to interesting results. Additionally, the MAC address can be randomized, which in should override the cache on the DHCP server and assign a new IP address. Extra requests can also be sent to exhaust the IP address range more quickly. Some of the more useful fields: * DHCP Server (the address of the server that responded) * Subnet Mask * Router * DNS Servers * Hostname ]] --- -- @args dhcptype The type of DHCP request to make. By default, DHCPINFORM is sent, but this -- argument can change it to DHCPOFFER, DHCPREQUEST, DHCPDECLINE, DHCPACK, DHCPNAK, -- DHCPRELEASE or DHCPINFORM. Not all types will evoke a response from all servers, -- and many require different fields to contain specific values. -- @args randomize_mac Set to true or 1 to send a random MAC address with -- the request (keep in mind that you may not see the response). This should -- cause the router to reserve a new IP address each time. -- @args requests Set to an integer to make up to that many requests (and display the results). -- -- @output -- Interesting ports on 192.168.1.1: -- PORT STATE SERVICE -- 67/udp open dhcps -- | dhcp-discover: -- | | DHCP Message Type: DHCPACK -- | | 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: 208.81.7.10, 208.81.7.14 -- -- -- 2011-12-28 - Revised by Patrik Karlsson -- o Removed DoS code and placed script into discovery and safe categories -- -- 2011-12-27 - Revised by Patrik Karlsson -- o Changed script to use DHCPINFORM instead of DHCPDISCOVER -- author = "Ron Bowes" license = "Same as Nmap--See http://nmap.org/book/man-legal.html" categories = {"discovery", "safe"} -- We want to run against a specific host if UDP/67 is open function portrule(host, port) if nmap.address_family() ~= 'inet' then stdnse.print_debug("%s is IPv4 compatible only.", SCRIPT_NAME) return false end return shortport.portnumber(67, "udp")(host, port) end local function go(host, port) -- Build and send a DHCP request using the specified request type, or DHCPINFORM local requests = tonumber(nmap.registry.args.requests or 1) local results = {} for i = 1, requests, 1 do -- Decide which type of request to make local request_type = dhcp.request_types[nmap.registry.args.dhcptype or "DHCPINFORM"] if(request_type == nil) then return false, "Valid request types: " .. stdnse.strjoin(", ", dhcp.request_types_str) end -- Generate the MAC address, if it's random local mac_addr = host.mac_addr_src if(nmap.registry.args.randomize_mac == 'true' or nmap.registry.args.randomize_mac == '1') then stdnse.print_debug(2, "dhcp-discover: Generating a random MAC address") mac_addr = "" for j=1, 6, 1 do mac_addr = mac_addr .. string.char(math.random(1, 255)) end end local iface, err = nmap.get_interface_info(host.interface) if ( not(iface) or not(iface.address) ) then return false, "Couldn't determine local ip for interface: " .. host.interface end local status, result = dhcp.make_request(host.ip, request_type, iface.address, mac_addr) if( not(status) ) then stdnse.print_debug(1, "dhcp-discover: Couldn't send DHCP request: %s", result) return false, result end table.insert(results, result) end -- Done! return true, results end action = function(host, port) local status, results = go(host, port) if(not(status)) then return stdnse.format_output(false, results) end if(not(results)) then return nil end -- Set the port state to open if(host) then nmap.set_port_state(host, port, "open") end local response = {} -- Display the results for i, result in ipairs(results) do local result_table = {} if ( nmap.registry.args.dhcptype and "DHCPINFORM" ~= nmap.registry.args.dhcptype ) then table.insert(result_table, string.format("IP Offered: %s", result.yiaddr_str)) end for _, v in ipairs(result.options) do if(type(v['value']) == 'table') then table.insert(result_table, string.format("%s: %s", v['name'], stdnse.strjoin(", ", v['value']))) else table.insert(result_table, string.format("%s: %s\n", v['name'], v['value'])) end end if(#results == 1) then response = result_table else result_table['name'] = string.format("Result %d of %d", i, #results) table.insert(response, result_table) end end return stdnse.format_output(true, response) end