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nmap/scripts/dhcp-discover.nse

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description = [[
Sends a DHCPDISCOVER request to a host on UDP port 67. The response
comes back to UDP port 68, and
is read using pcap (due to the inability for a script to choose its source port at the moment).
DHCPDISCOVER is a DHCP request that returns useful information from a DHCP server. 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 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.
DHCPINFORM is another type of DHCP request that requests the same information, but doesn't reserve
an address. Unfortunately, because many home routers simply ignore DHCPINFORM requests, we opted
to use DHCPDISCOVER instead.
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,
-- DHCPDISCOVER 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.
-- @args randomize_mac Set to <code>true</code> or <code>1</code> 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).
-- @args fake_requests Set to an integer to make that many fake requests
-- before the real one(s). This could be useful, for example, if you
-- also use <code>randomize_mac</code> and you want to try exhausting
-- all addresses.
-- @args timeout Set to an integer to use it for a timeout. My router
-- responds to <code>fake_requests</code> rate limited, at about 1
-- response/second. Therefore, timeout has to be at least
-- <code>fake_requests * 1000</code>. Default: 5000.
--
-- @output
-- Interesting ports on 192.168.1.1:
-- PORT STATE SERVICE
-- 67/udp open dhcps
-- | dhcp-discover:
-- | | IP Offered: 192.168.1.101
-- | | 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: 208.81.7.10, 208.81.7.14
--
-- The functions for creating and parsing DHCP requests are general, and
-- should be able to create and parse any DHCP request and response. If
-- other scripts require DHCP support, dhcp_build and dhcp_parse, with
-- their related functions, can easily be abstracted into a NSELib.
author = "Ron Bowes"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"default", "discovery", "intrusive"}
require 'bin'
require 'bit'
require 'ipOps'
require 'shortport'
require 'stdnse'
local request_types =
{
DHCPDISCOVER = 1,
DHCPOFFER = 2,
DHCPREQUEST = 3,
DHCPDECLINE = 4,
DHCPACK = 5,
DHCPNAK = 6,
DHCPRELEASE = 7,
DHCPINFORM = 8
}
local request_types_str = {}
request_types_str[1] = "DHCPDISCOVER"
request_types_str[2] = "DHCPOFFER"
request_types_str[3] = "DHCPREQUEST"
request_types_str[4] = "DHCPDECLINE"
request_types_str[5] = "DHCPACK"
request_types_str[6] = "DHCPNAK"
request_types_str[7] = "DHCPRELEASE"
request_types_str[8] = "DHCPINFORM"
portrule = shortport.portnumber(67, "udp")
callback = function(packetsz, layer2, layer3)
return string.sub(layer3, 33, 36)
end
---Read an IP address or a list of IP addresses. Print an error if the length isn't a multiple of 4.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_ip(data, pos, length)
if(length ~= 4) then
if((length % 4) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for an ip address (%d)", length)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 4 do
local value
pos, value = bin.unpack("<I", data, pos)
table.insert(results, ipOps.fromdword(value))
end
return pos, results
end
else
local value
pos, value = bin.unpack("<I", data, pos)
return pos, ipOps.fromdword(value)
end
end
---Read a string. The length of the string is given by the length field.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_string(data, pos, length)
return bin.unpack(string.format("A%d", length), data, pos)
end
---Read a single byte. Print an error if the length isn't 1.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_1_byte(data, pos, length)
if(length ~= 1) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 1)
pos = pos + length
return pos, nil
end
return bin.unpack("C", data, pos)
end
---Read a message type. This is a single-byte value that's looked up in the <code>request_types_str</code>
-- table. Print an error if the length isn't 1.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_message_type(data, pos, length)
local value
pos, value = read_1_byte(data, pos, length)
if(value == nil) then
stdnse.print_debug(1, "dhcp-discover: Couldn't read the 1-byte message type")
return pos, nil
end
return pos, request_types_str[value]
end
---Read a single byte, and return 'false' if it's 0, or 'true' if it's non-zero. Print an error if the
-- length isn't 1.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_boolean(data, pos, length)
local result
pos, result = read_1_byte(data, pos, length)
if(result == nil) then
stdnse.print_debug(1, "dhcp-discover: Couldn't read the 1-byte boolean")
return pos, nil
elseif(result == 0) then
return pos, "false"
else
return pos, "true"
end
end
---Read a 2-byte unsigned little endian value. Print an error if the length isn't 2.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_2_bytes(data, pos, length)
if(length ~= 2) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 2)
pos = pos + length
return pos, nil
end
return bin.unpack(">S", data, pos)
end
---Read a list of 2-byte unsigned little endian values. Print an error if the length isn't a multiple
-- of 2.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_2_bytes_list(data, pos, length)
if((length % 2) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be multiple of %d)", length, 2)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 2 do
local value
pos, value = bin.unpack(">S", data, pos)
table.insert(results, value)
end
return pos, results
end
end
---Read a 4-byte unsigned little endian value. Print an error if the length isn't 4.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_4_bytes(data, pos, length)
if(length ~= 4) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 4)
pos = pos + length
return pos, nil
end
return bin.unpack(">I", data, pos)
end
---Read a 4-byte unsigned little endian value, and interpret it as a time offset value. Print an
-- error if the length isn't 4.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_time(data, pos, length)
local result
if(length ~= 4) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 4)
pos = pos + length
return pos, nil
end
pos, result = bin.unpack(">I", data, pos)
-- This code was mostly taken from snmp-sysdescr.nse. It should probably be abstracted into stdnse.lua [TODO]
local days, hours, minutes, seconds, htime, mtime, stime
days = math.floor(result / 86400)
htime = math.fmod(result, 86400)
hours = math.floor(htime / 3600)
mtime = math.fmod(htime, 3600)
minutes = math.floor(mtime / 60)
seconds = math.fmod(mtime, 60)
local dayLabel
if days == 1 then
dayLabel = "day"
else
dayLabel = "days"
end
return pos, string.format("%d %s, %d:%02d:%02d", days, dayLabel, hours, minutes, seconds)
end
---Read a list of static routes. Each of them are a pair of IP addresses, a destination and a
-- router. Print an error if the length isn't a multiple of 8.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_static_route(data, pos, length)
if((length % 8) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be multiple of %d)", length, 8)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 8 do
local destination, router
pos, destination = read_ip(data, pos, 4)
pos, router = read_ip(data, pos, 4)
table.insert(results, {destination=destination, router=router})
end
return pos, results
end
end
---Read a list of policy filters. Each of them are a pair of IP addresses, an address and a
-- mask. Print an error if the length isn't a multiple of 8.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_policy_filter(data, pos, length)
if((length % 8) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be multiple of %d)", length, 8)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 8 do
local address, router
pos, address = read_ip(data, pos, 4)
pos, mask = read_ip(data, pos, 4)
table.insert(results, {address=address, mask=mask})
end
return pos, results
end
end
---These are the different fields for DHCP
local actions = {}
actions[1] = {name="Subnet Mask", func=read_ip, default=true}
actions[2] = {name="Time Offset", func=read_4_bytes, default=false}
actions[3] = {name="Router", func=read_ip, default=true}
actions[4] = {name="Time Server", func=read_ip, default=true}
actions[5] = {name="Name Server", func=read_ip, default=true}
actions[6] = {name="Domain Name Server", func=read_ip, default=true}
actions[7] = {name="Log Server", func=read_ip, default=true}
actions[8] = {name="Cookie Server", func=read_ip, default=true}
actions[9] = {name="LPR Server", func=read_ip, default=true}
actions[10] = {name="Impress Server", func=read_ip, default=true}
actions[11] = {name="Resource Location Server", func=read_ip, default=true}
actions[12] = {name="Hostname", func=read_string, default=true}
actions[13] = {name="Boot File Size", func=read_2_bytes, default=false}
actions[14] = {name="Merit Dump File", func=read_string, default=false}
actions[15] = {name="Domain Name", func=read_string, default=true}
actions[16] = {name="Swap Server", func=read_ip, default=true}
actions[17] = {name="Root Path", func=read_string, default=false}
actions[18] = {name="Extensions Path", func=read_string, default=false}
actions[19] = {name="IP Forwarding", func=read_boolean, default=false}
actions[20] = {name="Non-local Source Routing", func=read_boolean, default=true}
actions[21] = {name="Policy Filter", func=read_policy_filter, default=false}
actions[22] = {name="Maximum Datagram Reassembly Size",func=read_2_bytes, default=false}
actions[23] = {name="Default IP TTL", func=read_1_byte, default=false}
actions[24] = {name="Path MTU Aging Timeout", func=read_time, default=false}
actions[25] = {name="Path MTU Plateau", func=read_2_bytes_list, default=false}
actions[26] = {name="Interface MTU", func=read_2_bytes, default=false}
actions[27] = {name="All Subnets are Local", func=read_boolean, default=false}
actions[28] = {name="Broadcast Address", func=read_ip, default=true}
actions[29] = {name="Perform Mask Discovery", func=read_boolean, default=false}
actions[30] = {name="Mask Supplier", func=read_boolean, default=false}
actions[31] = {name="Perform Router Discovery", func=read_boolean, default=false}
actions[32] = {name="Router Solicitation Address", func=read_ip, default=true}
actions[33] = {name="Static Route", func=read_static_route, default=true}
actions[34] = {name="Trailer Encapsulation", func=read_boolean, default=false}
actions[35] = {name="ARP Cache Timeout", func=read_time, default=false}
actions[36] = {name="Ethernet Encapsulation", func=read_boolean, default=false}
actions[37] = {name="TCP Default TTL", func=read_1_byte, default=false}
actions[38] = {name="TCP Keepalive Interval", func=read_4_bytes, default=false}
actions[39] = {name="TCP Keepalive Garbage", func=read_boolean, default=false}
actions[40] = {name="NIS Domain", func=read_string, default=true}
actions[41] = {name="NIS Servers", func=read_ip, default=true}
actions[42] = {name="NTP Servers", func=read_ip, default=true}
actions[43] = {name="Vendor Specific Information", func=read_string, default=false}
actions[44] = {name="NetBIOS Name Server", func=read_ip, default=true}
actions[45] = {name="NetBIOS Datagram Server", func=read_ip, default=true}
actions[46] = {name="NetBIOS Node Type", func=read_1_byte, default=false}
actions[47] = {name="NetBIOS Scope", func=read_string, default=false}
actions[48] = {name="X Window Font Server", func=read_ip, default=true}
actions[49] = {name="X Window Display Manager", func=read_ip, default=true}
actions[50] = {name="Requested IP Address (client)", func=read_ip, default=false}
actions[51] = {name="IP Address Lease Time", func=read_time, default=false}
actions[52] = {name="Option Overload", func=read_1_byte, default=false}
actions[53] = {name="DHCP Message Type", func=read_message_type, default=false}
actions[54] = {name="Server Identifier", func=read_ip, default=true}
actions[55] = {name="Parameter Request List (client)", func=read_string, default=false}
actions[56] = {name="Error Message", func=read_string, default=true}
actions[57] = {name="Maximum DHCP Message Size", func=read_2_bytes, default=false}
actions[58] = {name="Renewal Time Value", func=read_time, default=false}
actions[59] = {name="Rebinding Time Value", func=read_time, default=false}
actions[60] = {name="Class Identifier", func=read_string, default=false}
actions[61] = {name="Client Identifier (client)", func=read_string, default=false}
---Build a DHCP packet.
--
--@param request_type The type of request (such as DHCPINFORM). See the <code>request_types</code>
-- table.
--@param ip_address The ip address (as a 4-byte string) where the server will send the response.
-- Generally, it'll be <code>host.bin_ip_src</code> or 255.255.255.255.
--@param mac_address The mac address (as a string no more than 16 bytes) where the server will
-- send the response. Generally, this will be <code>host.mac_addr_src</code> or
-- simply a blank string (""). The field will be padded to 16 bytes with null bytes.
--@param request_options [optional] The options to request from the server, as a string of bytes where each
-- byte represents a single option. For the types of options, see rfc2132. Some DHCP
-- servers (such as my Linksys WRT54g) will ignore this list and send whichever options
-- it wants. Options won't necessarily be honoured, it's up to the server what it sends
-- back. By default, all options (1..61) are requested.
--@param overrides [optional] A table of overrides. If a field in the table matches a field in the DHCP
-- packet (see rfc2131 section 2 for a list of possible fields. Or, just look at the
-- code.
--@param lease_time [optional] The lease time for which to request an IP. Default: 1 second.
--@return The packet, as a string. It should be sent to the server on UDP/67.
local function dhcp_build(request_type, ip_address, mac_address, request_options, overrides, lease_time)
local packet = ''
if(overrides == nil) then
overrides = {}
end
if(request_options == nil) then
-- Request the defaults, or there's no verbosity; otherwise, request everything!
request_options = ''
for i = 1, 61, 1 do
if(nmap.verbosity() > 0) then
request_options = request_options .. string.char(i)
else
if(actions[i] and actions[i].default) then
request_options = request_options .. string.char(i)
end
end
end
end
-- Header
packet = packet .. bin.pack(">CCCC", overrides['op'] or 1, overrides['htype'] or 1, overrides['hlen'] or 6, overrides['hops'] or 0) -- BOOTREQUEST, 10mb ethernet, 6 bytes long, 0 hops
packet = packet .. bin.pack(">I", overrides['xid'] or 0x4e4d4150) -- Transaction ID
packet = packet .. bin.pack(">SS", overrides['secs'] or 0, overrides['flags'] or 0x0000) -- Secs, flags
packet = packet .. bin.pack("A", ip_address) -- Client address
packet = packet .. bin.pack("<I", overrides['yiaddr'] or 0) -- yiaddr
packet = packet .. bin.pack("<I", overrides['siaddr'] or 0) -- siaddr
packet = packet .. bin.pack("<I", overrides['giaddr'] or 0) -- giaddr
packet = packet .. mac_address .. string.rep(string.char(0), 16 - #mac_address) -- chaddr (MAC address)
packet = packet .. (overrides['sname'] or string.rep(string.char(0), 64)) -- sname
packet = packet .. (overrides['file'] or string.rep(string.char(0), 128)) -- file
packet = packet .. bin.pack(">I", overrides['cookie'] or 0x63825363) -- Magic cookie
-- Options
packet = packet .. bin.pack(">CCC", 0x35, 1, request_type) -- Request type
packet = packet .. bin.pack(">CCA", 0x37, #request_options, request_options) -- Request options
packet = packet .. bin.pack(">CCI", 0x33, 4, lease_time or 1) -- Lease time
packet = packet .. bin.pack(">C", 0xFF) -- Termination
return packet
end
---Parse a DHCP packet (either a request or a response) and return the results as a table. The
-- table at the top of this function (<code>actions</code>) defines the name of each field, as
-- laid out in rfc2132, and the function that parses it.
--
-- In theory, this should be able to parse any valid DHCP packet.
--
--@param data The DHCP packet data. Any padding at the end of the packet will be ignored (by default,
-- DHCP packets are padded with \x00 bytes).
local function dhcp_parse(data)
local pos = 1
local result = {}
-- Receive the first bit and make sure we got the correct operation back
pos, result['op'], result['htype'], result['hlen'], result['hops'] = bin.unpack(">CCCC", data, pos)
if(result['op'] ~= 2) then
return false, string.format("DHCP server returned invalid reply ('op' wasn't BOOTREPLY (it was 0x%02x))", result['op'])
end
-- Confirm the transaction id
pos, result['xid'] = bin.unpack(">I", data, pos)
if(result['xid'] ~= 0x4e4d4150) then
return false, string.format("DHCP server returned invalid reply (transaction id didn't match (0x%08x != ))", result['xid'], 0x4e4d4150)
end
-- Unpack the secs, flags, addresses, sname, and file
pos, result['secs'], result['flags'] = bin.unpack(">SS", data, pos)
pos, result['ciaddr'] = bin.unpack("<I", data, pos)
pos, result['yiaddr'] = bin.unpack("<I", data, pos)
pos, result['siaddr'] = bin.unpack("<I", data, pos)
pos, result['giaddr'] = bin.unpack("<I", data, pos)
pos, result['chaddr'] = bin.unpack("A16", data, pos)
pos, result['sname'] = bin.unpack("A64", data, pos)
pos, result['file'] = bin.unpack("A128", data, pos)
-- Convert the addresses to strings
result['ciaddr_str'] = ipOps.fromdword(result['ciaddr'])
result['yiaddr_str'] = ipOps.fromdword(result['yiaddr'])
result['siaddr_str'] = ipOps.fromdword(result['siaddr'])
result['giaddr_str'] = ipOps.fromdword(result['giaddr'])
-- Confirm the cookie
pos, result['cookie'] = bin.unpack(">I", data, pos)
if(result['cookie'] ~= 0x63825363) then
return false, "DHCP server returned invalid reply (the magic cookie was invalid)"
end
-- Parse the options
result['options'] = {}
while true do
local option, length
pos, option, length = bin.unpack(">CC", data, pos)
-- Check for termination condition
if(option == 0xFF) then
break;
end
-- Get the action from the array, based on the code
local action = actions[option]
-- Verify we got a valid code (if we didn't, we're probably in big trouble)
if(action == nil) then
stdnse.print_debug(1, "dhcp-discover: Unknown option: %d", option)
pos = pos + length
else
-- Call the function to parse the option, and insert the result into our results table
local value
stdnse.print_debug(2, "dhcp-discover: Attempting to parse %s", action['name'])
pos, value = action['func'](data, pos, length)
if(nmap.verbosity() == 0 and action.default == false) then
stdnse.print_debug(1, "dhcp-discover: Server returned unrequested option (%s => %s)", action['name'], value)
else
if(value) then
table.insert(result['options'], {name=action['name'], value=value})
else
stdnse.print_debug(1, "dhcp-discover: Couldn't determine value for %s", action['name']);
end
end
end
-- Handle the 'Option Overload' option specially -- if it's set, it tells us to use the file and/or sname values after we
-- run out of data.
if(option == 52) then
if(value == 1) then
data = data .. result['file']
elseif(value == 2) then
data = data .. result['sname']
elseif(value == 3) then
data = data .. result['file'] .. result['sname']
else
stdnse.print_debug(1, "dhcp-discover: Warning: 'Option Overload' gave an unsupported value: %d", value)
end
end
end
return true, result
end
local function go(host, port)
local pcap, socket
local status, err, data
local result
local results = {}
local timeout = 5000
if(nmap.registry.args.timeout) then
timeout = tonumber(nmap.registry.args.timeout)
end
local requests = 1
if(nmap.registry.args.requests) then
requests = tonumber(nmap.registry.args.requests)
end
-- Verify we have a IPv4 address
if(string.len(host.bin_ip_src) ~= 4) then
return false, "Sorry, dhcp-discover only supports IPv4!"
end
-- Verify we have a MAC address
if(string.len(host.mac_addr_src) ~= 6) then
return false, "Sorry, dhcp-discover only supports Ethernet!"
end
-- Create a pcap socket to listen for the response (this is a HUGE hack. TODO: Fix once I can set the source port)
pcap = nmap.new_socket()
pcap:pcap_open(host.interface, 590, 0, callback, "udp port 68")
stdnse.print_debug(1, "dhcp-discover: Setting socket timeout to %ds", timeout)
pcap:set_timeout(timeout)
-- Create the UDP socket
socket = nmap.new_socket()
status, err = socket:connect(host.ip, port.number, "udp")
if(status == false) then
return false, "Couldn't create socket: " .. err
end
-- We're going to need some low quality random numbers
math.randomseed(os.time())
-- Create fake requests if the user asked to. These are fired and forgotten, we ignore the responses.
if(nmap.registry.args.fake_requests) then
for i=1, tonumber(nmap.registry.args.fake_requests), 1 do
-- Build and send a DHCP request using the specified request type, or DHCPDISCOVER
local request_type = request_types[nmap.registry.args.dhcptype or "DHCPDISCOVER"]
if(request_type == nil) then
return false, "Valid request types: " .. stdnse.strjoin(", ", 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
-- Build and send the packet
local response = dhcp_build(request_type, host.bin_ip_src, mac_addr, nil, {xid=i})
socket:send(response)
end
end
-- Build and send a DHCP request using the specified request type, or DHCPDISCOVER
for i = 1, requests, 1 do
-- Register the packet cap
pcap:pcap_register("NMAP")
-- Decide which type of request to make
local request_type = request_types[nmap.registry.args.dhcptype or "DHCPDISCOVER"]
if(request_type == nil) then
return false, "Valid request types: " .. stdnse.strjoin(", ", 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
-- Build and send the packet
stdnse.print_debug(2, "dhcp-discover: Sending DHCP request #%d", i)
local response = dhcp_build(request_type, host.bin_ip_src, mac_addr)
socket:send(response)
-- Receive the result
status, err, _, data = pcap:pcap_receive()
if(status == false) then
stdnse.print_debug(1, "dhcp-discover: Error calling pcap_receive(): %s", err)
return false, "Error calling pcap_receive(): " .. err
end
-- If no data was captured (ie, a timeout), return what, if anything, we have
if(data == nil) then
stdnse.print_debug(1, "dhcp-discover: Error calling pcap_receive(): TIMEOUT")
if(#results > 0) then
return true, results
else
return false, "Error calling pcap_receive(): TIMEOUT"
end
end
-- Cut off the address/transport headers
data = string.sub(data, 29) -- I doubt this is the right way to do this, but since we're only supporting IPv4 + UDP, maybe it'll work?
-- Parse the result
status, result = dhcp_parse(data)
if(status == false) then
stdnse.print_debug(1, "dhcp-discover: Couldn't parse DHCP packet: %s", result)
return false, "Couldn't parse DHCP packet: " .. result
end
table.insert(results, result)
end
socket:close()
-- Done!
return true, results
end
action = function(host, port)
local status, results = go(host, port)
if(status == false) then
return stdnse.format_output(false, results)
end
if(results == nil) then
return nil
end
-- Set the port state to open
nmap.set_port_state(host, port, "open")
local response = {}
-- Display the results
for i, result in ipairs(results) do
if(#results ~= 1) then
table.insert(response, string.format("Result %d", i))
end
table.insert(response, string.format("IP Offered: %s", result.yiaddr_str))
for _, v in ipairs(result.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
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