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---
-- Simple DNS library supporting packet creation, encoding, decoding,
-- and querying.
--
-- The most common interface to this module are the <code>query</code> and
-- <code>reverse</code> functions. <code>query</code> performs a DNS query,
-- and <code>reverse</code> prepares an ip address to have a reverse query
-- performed.
--
-- <code>query</code> takes two options - a domain name to look up and an
-- optional table of options. For more information on the options table,
-- see the documentation for <code>query</code>.
--
-- Example usage:
-- <code>
-- -- After this call, <code>status</code> is <code>true</code> and <code>result</code> is <code>"72.14.204.104"</code>
-- local status, result = dns.query('www.google.ca')
--
-- -- After this call, <code>status</code> is <code>false</code> and <code>result</code> is <code>"No such name"</code>
-- local status, result = dns.query('www.google.abc')
--
-- -- After this call, <code>status</code> is <code>true</code> and <code>result</code> is the table <code>{"72.14.204.103", "72.14.204.104", "72.14.204.147", "72.14.204.99"}</code>
-- local status, result = dns.query('www.google.ca', {retAll=true})
--
-- -- After this call, <code>status</code> is <code>true</code> and <code>result</code> is the <code>"2001:19f0:0:0:0:dead:beef:cafe"</code>
-- local status, result = dns.query('irc.ipv6.efnet.org', {dtype='AAAA'})
--</code>
--
--
-- @copyright Same as Nmap--See http://nmap.org/book/man-legal.html
module(... or "dns", package.seeall)
require("bit")
require("ipOps")
require("stdnse")
get_servers = nmap.get_dns_servers
---
-- Table of DNS resource types.
-- @name types
-- @class table
types = {
A = 1,
NS = 2,
SOA = 6,
CNAME = 5,
PTR = 12,
HINFO = 13,
MX = 15,
TXT = 16,
AAAA = 28,
SRV = 33,
OPT = 41,
SSHFP = 44,
NSEC = 47,
AXFR = 252,
ANY = 255
}
CLASS = {
IN = 1,
CH = 3,
ANY = 255
}
---
-- Repeatedly sends UDP packets to host, waiting for an answer.
-- @param data Data to be sent.
-- @param host Host to connect to.
-- @param port Port to connect to.
-- @param timeout Number of ms to wait for a response.
-- @param cnt Number of tries.
-- @param multiple If true, keep reading multiple responses until timeout.
-- @return Status (true or false).
-- @return Response (if status is true).
local function sendPackets(data, host, port, timeout, cnt, multiple)
local socket = nmap.new_socket("udp")
local responses = {}
socket:set_timeout(timeout)
if ( not(multiple) ) then
socket:connect( host, port, "udp" )
end
for i = 1, cnt do
local status, err
if ( multiple ) then
status, err = socket:sendto(host, port, data)
else
status, err = socket:send(data)
end
if (not(status)) then return false, err end
local response
if ( multiple ) then
while(true) do
status, response = socket:receive()
if( not(status) ) then break end
local status, _, _, ip, _ = socket:get_info()
table.insert(responses, { data = response, peer = ip } )
end
else
status, response = socket:receive()
if ( status ) then
local status, _, _, ip, _ = socket:get_info()
table.insert(responses, { data = response, peer = ip } )
end
end
if (#responses>0) then
socket:close()
return true, responses
end
end
socket:close()
return false
end
---
-- Checks if a DNS response packet contains a useful answer.
-- @param rPkt Decoded DNS response packet.
-- @return True if useful, false if not.
local function gotAnswer(rPkt)
-- have we even got answers?
if #rPkt.answers > 0 then
-- some MDNS implementation incorrectly return an empty question section
-- if this is the case return true
if rPkt.questions[1] == nil then
return true
end
-- are those answers not just cnames?
if rPkt.questions[1].dtype == types.A then
for _, v in ipairs(rPkt.answers) do
-- if at least one answer is an A record, it's an answer
if v.dtype == types.A then
return true
end
end
-- if none was an A record, it's not really an answer
return false
else -- there was no A request, CNAMEs are not of interest
return true
end
-- no such name is the answer
elseif rPkt.flags.RC3 and rPkt.flags.RC4 then
return true
-- really no answer
else
return false
end
end
---
-- Tries to find the next nameserver with authority to get a result for
-- query.
-- @param rPkt Decoded DNS response packet
-- @return String or table of next server(s) to query, or false.
local function getAuthDns(rPkt)
if #rPkt.auth == 0 then
if #rPkt.answers == 0 then
return false
else
if rPkt.answers[1].dtype == types.CNAME then
return {cname = rPkt.answers[1].domain}
end
end
end
if rPkt.auth[1].dtype == types.NS then
if #rPkt.add > 0 then
local hosts = {}
for _, v in ipairs(rPkt.add) do
if v.dtype == types.A then
table.insert(hosts, v.ip)
end
end
if #hosts > 0 then return hosts end
end
local status, next = query(rPkt.auth[1].domain, {dtype = "A" })
return next
end
return false
end
local function processResponse( response, dname, dtype, options )
local rPkt = decode(response)
-- is it a real answer?
if gotAnswer(rPkt) then
if (options.retPkt) then
return true, rPkt
else
return findNiceAnswer(dtype, rPkt, options.retAll)
end
else -- if not, ask the next server in authority
local next_server = getAuthDns(rPkt)
-- if we got a CNAME, ask for the CNAME
if type(next_server) == 'table' and next_server.cname then
options.tries = options.tries - 1
return query(next_server.cname, options)
end
-- only ask next server in authority, if
-- we got an auth dns and
-- it isn't the one we just asked
if next_server and next_server ~= options.host and options.tries > 1 then
options.host = next_server
options.tries = options.tries - 1
return query(dname, options)
end
end
-- nothing worked
stdnse.print_debug(1, "dns.query() failed to resolve the requested query%s%s", dname and ": " or ".", dname or "")
return false, "No Answers"
end
---
-- Query DNS servers for a DNS record.
-- @param dname Desired domain name entry.
-- @param options A table containing any of the following fields:
-- * <code>dtype</code>: Desired DNS record type (default: <code>"A"</code>).
-- * <code>host</code>: DNS server to be queried (default: DNS servers known to Nmap).
-- * <code>port</code>: Port of DNS server to connect to (default: <code>53</code>).
-- * <code>tries</code>: How often should <code>query</code> try to contact another server (for non-recursive queries).
-- * <code>retAll</code>: Return all answers, not just the first.
-- * <code>retPkt</code>: Return the packet instead of using the answer-fetching mechanism.
-- * <code>norecurse</code>: If true, do not set the recursion (RD) flag.
-- * <code>multiple</code>: If true, expects multiple hosts to respond to multicast request
-- * <code>flags</code>: numeric value to set flags in the DNS query to a specific value
-- * <code>id</code>: numeric value to use for the DNS transaction id
-- @return <code>true</code> if a dns response was received and contained an answer of the requested type,
-- or the decoded dns response was requested (retPkt) and is being returned - or <code>false</code> otherwise.
-- @return String answer of the requested type, table of answers or a String error message of one of the following:
-- "No Such Name", "No Servers", "No Answers", "Unable to handle response"
function query(dname, options)
if not options then options = {} end
local dtype, host, port = options.dtype, options.host, options.port
local class = options.class or CLASS.IN
if not options.tries then options.tries = 10 end -- don't get into an infinite loop
if not options.sendCount then options.sendCount = 2 end
if type( options.timeout ) ~= "number" then options.timeout = get_default_timeout() end
if type(dtype) == "string" then
dtype = types[dtype]
end
if not dtype then dtype = types.A end
local srv
local srvI = 1
if not port then port = 53 end
if not host then
srv = get_servers()
if srv and srv[1] then
host = srv[1]
else
return false, "No Servers"
end
elseif type(host) == "table" then
srv = host
host = srv[1]
end
local pkt = newPacket()
addQuestion(pkt, dname, dtype, class)
if options.norecurse then pkt.flags.RD = false end
if ( options.dnssec ) then
if ( options.nsid ) then
addNSID(pkt, {DO = true})
elseif ( options.client_subnet) then
add_client_subnet(pkt, {DO = true}, options.client_subnet)
else
addOPT(pkt, {DO = true})
end
elseif ( options.nsid ) then
addNSID(pkt, {})
elseif ( options.client_subnet) then
add_client_subnet(pkt, {}, options.client_subnet)
end
if ( options.flags ) then pkt.flags.raw = options.flags end
if ( options.id ) then pkt.id = options.id end
local data = encode(pkt)
local status, response = sendPackets(data, host, port, options.timeout, options.sendCount, options.multiple)
-- if working with know nameservers, try the others
while((not status) and srv and srvI < #srv) do
srvI = srvI + 1
host = srv[srvI]
status, response = sendPackets(data, host, port, options.timeout, options.sendCount)
end
-- if we got any response:
if status then
if ( options.multiple ) then
local multiresponse = {}
for _, r in ipairs( response ) do
local status, presponse = processResponse( r.data, dname, dtype, options )
if( status ) then
table.insert( multiresponse, { ['output']=presponse, ['peer']=r.peer } )
end
end
return true, multiresponse
else
return processResponse( response[1].data, dname, dtype, options)
end
else
stdnse.print_debug(1, "dns.query() got zero responses attempting to resolve query%s%s", dname and ": " or ".", dname or "")
return false, "No Answers"
end
end
---
-- Formats an IP address for reverse lookup.
-- @param ip IP address string.
-- @return "Domain"-style representation of IP as subdomain of in-addr.arpa or
-- ip6.arpa.
function reverse(ip)
ip = ipOps.expand_ip(ip)
if type(ip) ~= "string" then return nil end
local delim = "%."
local arpa = ".in-addr.arpa"
if ip:match(":") then
delim = ":"
arpa = ".ip6.arpa"
end
local ipParts = stdnse.strsplit(delim, ip)
if #ipParts == 8 then
-- padding
local mask = "0000"
for i, part in ipairs(ipParts) do
ipParts[i] = mask:sub(1, #mask - #part) .. part
end
-- 32 parts from 8
local temp = {}
for i, hdt in ipairs(ipParts) do
for part in hdt:gmatch("%x") do
temp[#temp+1] = part
end
end
ipParts = temp
end
local ipReverse = {}
for i = #ipParts, 1, -1 do
table.insert(ipReverse, ipParts[i])
end
return table.concat(ipReverse, ".") .. arpa
end
-- Table for answer fetching functions.
local answerFetcher = {}
-- Answer fetcher for TXT records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns TXT record or Table of TXT records or String Error message.
answerFetcher[types.TXT] = function(dec, retAll)
local answers = {}
if not retAll and dec.answers[1].data then
return true, string.sub(dec.answers[1].data, 2)
elseif not retAll then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: TXT")
return false, "No Answers"
else
for _, v in ipairs(dec.answers) do
if v.TXT and v.TXT.text then
for _, v in ipairs( v.TXT.text ) do
table.insert(answers, v)
end
end
end
end
if #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: TXT")
return false, "No Answers"
end
return true, answers
end
-- Answer fetcher for A records
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns A record or Table of A records or String Error message.
answerFetcher[types.A] = function(dec, retAll)
local answers = {}
for _, ans in ipairs(dec.answers) do
if ans.dtype == types.A then
if not retAll then
return true, ans.ip
end
table.insert(answers, ans.ip)
end
end
if not retAll or #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: A")
return false, "No Answers"
end
return true, answers
end
-- Answer fetcher for CNAME records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first Domain entry or Table of domain entries or String Error message.
answerFetcher[types.CNAME] = function(dec, retAll)
local answers = {}
if not retAll and dec.answers[1].domain then
return true, dec.answers[1].domain
elseif not retAll then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: NS, PTR or CNAME")
return false, "No Answers"
else
for _, v in ipairs(dec.answers) do
if v.domain then table.insert(answers, v.domain) end
end
end
if #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: NS, PTR or CNAME")
return false, "No Answers"
end
return true, answers
end
-- Answer fetcher for MX records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns MX record or Table of MX records or String Error message.
-- Note that the format of a returned MX answer is "preference:hostname:IPaddress" where zero
-- or more IP addresses may be present.
answerFetcher[types.MX] = function(dec, retAll)
local mx, ip, answers = {}, {}, {}
for _, ans in ipairs(dec.answers) do
if ans.MX then mx[#mx+1] = ans.MX end
if not retAll then break end
end
if #mx == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: MX")
return false, "No Answers"
end
for _, add in ipairs(dec.add) do
if ip[add.dname] then table.insert(ip[add.dname], add.ip)
else ip[add.dname] = {add.ip} end
end
for _, mxrec in ipairs(mx) do
if ip[mxrec.server] then
table.insert( answers, ("%s:%s:%s"):format(mxrec.pref or "-", mxrec.server or "-", table.concat(ip[mxrec.server], ":")) )
if not retAll then return true, answers[1] end
else
-- no IP ?
table.insert( answers, ("%s:%s"):format(mxrec.pref or "-", mxrec.server or "-") )
if not retAll then return true, answers[1] end
end
end
return true, answers
end
-- Answer fetcher for SRV records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns SRV record or Table of SRV records or String Error message.
-- Note that the format of a returned SRV answer is "priority:weight:port:target" where zero
-- or more IP addresses may be present.
answerFetcher[types.SRV] = function(dec, retAll)
local srv, ip, answers = {}, {}, {}
for _, ans in ipairs(dec.answers) do
if ans.dtype == types.SRV then
if not retAll then
return true, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target )
end
table.insert( answers, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target ) )
end
end
if #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: SRV")
return false, "No Answers"
end
return true, answers
end
-- Answer fetcher for NSEC records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns NSEC record or Table of NSEC records or String Error message.
-- Note that the format of a returned NSEC answer is "name:dname:types".
answerFetcher[types.NSEC] = function(dec, retAll)
local nsec, answers = {}, {}
for _, auth in ipairs(dec.auth) do
if auth.NSEC then nsec[#nsec+1] = auth.NSEC end
if not retAll then break end
end
if #nsec == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: NSEC")
return false, "No Answers"
end
for _, nsecrec in ipairs(nsec) do
table.insert( answers, ("%s:%s:%s"):format(nsecrec.name or "-", nsecrec.dname or "-", stdnse.strjoin(":", nsecrec.types) or "-"))
end
if not retAll then return true, answers[1] end
return true, answers
end
-- Answer fetcher for NS records.
-- @name answerFetcher[types.NS]
-- @class function
-- @param dec Decoded DNS response.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first Domain entry or Table of domain entries or String Error message.
answerFetcher[types.NS] = answerFetcher[types.CNAME]
-- Answer fetcher for PTR records.
-- @name answerFetcher[types.PTR]
-- @class function
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first Domain entry or Table of domain entries or String Error message.
answerFetcher[types.PTR] = answerFetcher[types.CNAME]
-- Answer fetcher for AAAA records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns AAAA record or Table of AAAA records or String Error message.
answerFetcher[types.AAAA] = function(dec, retAll)
local answers = {}
for _, ans in ipairs(dec.answers) do
if ans.dtype == types.AAAA then
if not retAll then
return true, ans.ipv6
end
table.insert(answers, ans.ipv6)
end
end
if not retAll or #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: AAAA")
return false, "No Answers"
end
return true, answers
end
---Calls the answer fetcher for <code>dtype</code> or returns an error code in
-- case of a "no such name" error.
--
-- @param dtype DNS resource record type.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return Answer according to the answer fetcher for <code>dtype</code> or an Error message.
function findNiceAnswer(dtype, dec, retAll)
if (#dec.answers > 0) then
if answerFetcher[dtype] then
return answerFetcher[dtype](dec, retAll)
else
stdnse.print_debug(1, "dns.findNiceAnswer() does not have an answerFetcher for dtype %s", tostring(dtype))
return false, "Unable to handle response"
end
elseif (dec.flags.RC3 and dec.flags.RC4) then
return false, "No Such Name"
else
stdnse.print_debug(1, "dns.findNiceAnswer() found zero answers in a response, but got an unexpected flags.replycode")
return false, "No Answers"
end
end
-- Table for additional fetching functions.
-- Some servers return their answers in the additional section. The
-- findNiceAdditional function with its relevant additionalFetcher functions
-- addresses this. This unfortunately involved some code duplication (because
-- of current design of the dns library) from the answerFetchers to the
-- additionalFetchers.
local additionalFetcher = {}
-- Additional fetcher for TXT records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns TXT record or Table of TXT records or String Error message.
additionalFetcher[types.TXT] = function(dec, retAll)
local answers = {}
if not retAll and dec.add[1].data then
return true, string.sub(dec.add[1].data, 2)
elseif not retAll then
stdnse.print_debug(1, "dns.aditionalFetcher found no records of the required type: TXT")
return false, "No Answers"
else
for _, v in ipairs(dec.add) do
if v.TXT and v.TXT.text then
for _, v in ipairs( v.TXT.text ) do
table.insert(answers, v)
end
end
end
end
if #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: TXT")
return false, "No Answers"
end
return true, answers
end
-- Additional fetcher for A records
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns A record or Table of A records or String Error message.
additionalFetcher[types.A] = function(dec, retAll)
local answers = {}
for _, ans in ipairs(dec.add) do
if ans.dtype == types.A then
if not retAll then
return true, ans.ip
end
table.insert(answers, ans.ip)
end
end
if not retAll or #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: A")
return false, "No Answers"
end
return true, answers
end
-- Additional fetcher for SRV records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns SRV record or Table of SRV records or String Error message.
-- Note that the format of a returned SRV answer is "priority:weight:port:target" where zero
-- or more IP addresses may be present.
additionalFetcher[types.SRV] = function(dec, retAll)
local srv, ip, answers = {}, {}, {}
for _, ans in ipairs(dec.add) do
if ans.dtype == types.SRV then
if not retAll then
return true, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target )
end
table.insert( answers, ("%s:%s:%s:%s"):format( ans.SRV.prio, ans.SRV.weight, ans.SRV.port, ans.SRV.target ) )
end
end
if #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: SRV")
return false, "No Answers"
end
return true, answers
end
-- Additional fetcher for AAAA records.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return String first dns AAAA record or Table of AAAA records or String Error message.
additionalFetcher[types.AAAA] = function(dec, retAll)
local answers = {}
for _, ans in ipairs(dec.add) do
if ans.dtype == types.AAAA then
if not retAll then
return true, ans.ipv6
end
table.insert(answers, ans.ipv6)
end
end
if not retAll or #answers == 0 then
stdnse.print_debug(1, "dns.answerFetcher found no records of the required type: AAAA")
return false, "No Answers"
end
return true, answers
end
---
-- Calls the answer fetcher for <code>dtype</code> or returns an error code in
-- case of a "no such name" error.
-- @param dtype DNS resource record type.
-- @param dec Decoded DNS response.
-- @param retAll If true, return all entries, not just the first.
-- @return True if one or more answers of the required type were found - otherwise false.
-- @return Answer according to the answer fetcher for <code>dtype</code> or an Error message.
function findNiceAdditional(dtype, dec, retAll)
if (#dec.add > 0) then
if additionalFetcher[dtype] then
return additionalFetcher[dtype](dec, retAll)
else
stdnse.print_debug(1, "dns.findNiceAdditional() does not have an additionalFetcher for dtype %s",
(type(dtype) == 'string' and dtype) or type(dtype) or "nil")
return false, "Unable to handle response"
end
elseif (dec.flags.RC3 and dec.flags.RC4) then
return false, "No Such Name"
else
stdnse.print_debug(1, "dns.findNiceAdditional() found zero answers in a response, but got an unexpected flags.replycode")
return false, "No Answers"
end
end
--
-- Encodes a FQDN
-- @param fqdn containing the fully qualified domain name
-- @return encQ containing the encoded value
local function encodeFQDN(fqdn)
if ( not(fqdn) or #fqdn == 0 ) then return end
local parts = stdnse.strsplit("%.", fqdn)
local encQ = ""
for _, part in ipairs(parts) do
encQ = encQ .. bin.pack("p", part)
end
encQ = encQ .. string.char(0)
return encQ
end
---
-- Encodes the question part of a DNS request.
-- @param questions Table of questions.
-- @return Encoded question string.
local function encodeQuestions(questions)
if type(questions) ~= "table" then return nil end
local encQ = ""
for _, v in ipairs(questions) do
encQ = encQ .. encodeFQDN(v.dname)
encQ = encQ .. bin.pack(">SS", v.dtype, v.class)
end
return encQ
end
---
-- Encodes the zone part of a DNS request.
-- @param questions Table of questions.
-- @return Encoded question string.
local function encodeZones(zones)
return encodeQuestions(zones)
end
local function encodeUpdates(updates)
if type(updates) ~= "table" then return nil end
local encQ = ""
for _, v in ipairs(updates) do
encQ = encQ .. encodeFQDN(v.dname)
encQ = encQ .. bin.pack(">SSISA", v.dtype, v.class, v.ttl, #v.data, v.data)
end
return encQ
end
---
-- Encodes the additional part of a DNS request.
-- @param additional Table of additional records. Each must have the keys
-- <code>type</code>, <code>class</code>, <code>ttl</code>, <code>rdlen</code>,
-- and <code>rdata</code>.
-- @return Encoded additional string.
local function encodeAdditional(additional)
if type(additional) ~= "table" then return nil end
local encA = ""
for _, v in ipairs(additional) do
encA = encA .. bin.pack(">xSSISA", v.type, v.class, v.ttl, v.rdlen, v.rdata)
end
return encA
end
---
-- Encodes DNS flags to a binary digit string.
-- @param flags Flag table, each entry representing a flag (QR, OCx, AA, TC, RD,
-- RA, RCx).
-- @return Binary digit string representing flags.
local function encodeFlags(flags)
if type(flags) == "string" then return flags end
if type(flags) ~= "table" then return nil end
local fb = ""
if flags.QR then fb = fb .. "1" else fb = fb .. "0" end
if flags.OC1 then fb = fb .. "1" else fb = fb .. "0" end
if flags.OC2 then fb = fb .. "1" else fb = fb .. "0" end
if flags.OC3 then fb = fb .. "1" else fb = fb .. "0" end
if flags.OC4 then fb = fb .. "1" else fb = fb .. "0" end
if flags.AA then fb = fb .. "1" else fb = fb .. "0" end
if flags.TC then fb = fb .. "1" else fb = fb .. "0" end
if flags.RD then fb = fb .. "1" else fb = fb .. "0" end
if flags.RA then fb = fb .. "1" else fb = fb .. "0" end
fb = fb .. "000"
if flags.RC1 then fb = fb .. "1" else fb = fb .. "0" end
if flags.RC2 then fb = fb .. "1" else fb = fb .. "0" end
if flags.RC3 then fb = fb .. "1" else fb = fb .. "0" end
if flags.RC4 then fb = fb .. "1" else fb = fb .. "0" end
return fb
end
---
-- Encode a DNS packet.
--
-- Caution: doesn't encode answer and authority part.
-- @param pkt Table representing DNS packet, initialized by
-- <code>newPacket</code>.
-- @return Encoded DNS packet.
function encode(pkt)
if type(pkt) ~= "table" then return nil end
local encFlags = encodeFlags(pkt.flags)
local additional = encodeAdditional(pkt.additional)
local aorplen = #pkt.answers
local data, qorzlen, aorulen
if ( #pkt.questions > 0 ) then
data = encodeQuestions( pkt.questions )
qorzlen = #pkt.questions
aorulen = 0
else
-- The packet has no questions, assume we're dealing with an update
data = encodeZones( pkt.zones ) .. encodeUpdates( pkt.updates )
qorzlen = #pkt.zones
aorulen = #pkt.updates
end
local encStr
if ( pkt.flags.raw ) then
encStr = bin.pack(">SSS4", pkt.id, pkt.flags.raw, qorzlen, aorplen, aorulen, #pkt.additional) .. data .. additional
else
encStr = bin.pack(">SBS4", pkt.id, encFlags, qorzlen, aorplen, aorulen, #pkt.additional) .. data .. additional
end
return encStr
end
---
-- Decodes a domain in a DNS packet. Handles "compressed" data too.
-- @param data Complete DNS packet.
-- @param pos Starting position in packet.
-- @return Position after decoding.
-- @return Decoded domain, or <code>nil</code> on error.
function decStr(data, pos)
local function dec(data, pos, limit)
local partlen
local parts = {}
local part
-- Avoid infinite recursion on malformed compressed messages.
limit = limit or 10
if limit < 0 then
return pos, nil
end
pos, partlen = bin.unpack(">C", data, pos)
while (partlen ~= 0) do
if (partlen < 64) then
pos, part = bin.unpack("A" .. partlen, data, pos)
if part == nil then
return pos
end
table.insert(parts, part)
pos, partlen = bin.unpack(">C", data, pos)
else
pos, partlen = bin.unpack(">S", data, pos - 1)
local _, part = dec(data, partlen - 0xC000 + 1, limit - 1)
if part == nil then
return pos
end
table.insert(parts, part)
partlen = 0
end
end
return pos, table.concat(parts, ".")
end
return dec(data, pos)
end
---
-- Decodes questions in a DNS packet.
-- @param data Complete DNS packet.
-- @param count Value of question counter in header.
-- @param pos Starting position in packet.
-- @return Position after decoding.
-- @return Table of decoded questions.
local function decodeQuestions(data, count, pos)
local q = {}
for i = 1, count do
local currQ = {}
pos, currQ.dname = decStr(data, pos)
pos, currQ.dtype, currQ.class = bin.unpack(">SS", data, pos)
table.insert(q, currQ)
end
return pos, q
end
---
-- Table of functions to decode resource records
local decoder = {}
-- Decodes IP of A record, puts it in <code>entry.ip</code>.
-- @param entry RR in packet.
decoder[types.A] = function(entry)
local ip = {}
local _
_, ip[1], ip[2], ip[3], ip[4] = bin.unpack(">C4", entry.data)
entry.ip = table.concat(ip, ".")
end
-- Decodes IP of AAAA record, puts it in <code>entry.ipv6</code>.
-- @param entry RR in packet.
decoder[types.AAAA] = function(entry)
local ip = {}
local pos = 1
local num
for i = 1, 8 do
pos, num = bin.unpack(">S", entry.data, pos)
table.insert(ip, string.format('%x', num))
end
entry.ipv6 = table.concat(ip, ":")
end
-- Decodes SSH fingerprint record, puts it in <code>entry.SSHFP</code> as
-- defined in RFC 4255.
--
-- <code>entry.SSHFP</code> has the fields <code>algorithm</code>,
-- <code>fptype</code>, and <code>fingerprint</code>.
-- @param entry RR in packet.
decoder[types.SSHFP] = function(entry)
local _
entry.SSHFP = {}
_, entry.SSHFP.algorithm,
entry.SSHFP.fptype, entry.SSHFP.fingerprint = bin.unpack(">C2H" .. (#entry.data - 2), entry.data)
end
-- Decodes SOA record, puts it in <code>entry.SOA</code>.
--
-- <code>entry.SOA</code> has the fields <code>mname</code>, <code>rname</code>,
-- <code>serial</code>, <code>refresh</code>, <code>retry</code>,
-- <code>expire</code>, and <code>minimum</code>.
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.SOA] = function(entry, data, pos)
local np = pos - #entry.data
entry.SOA = {}
np, entry.SOA.mname = decStr(data, np)
np, entry.SOA.rname = decStr(data, np)
np, entry.SOA.serial,
entry.SOA.refresh,
entry.SOA.retry,
entry.SOA.expire,
entry.SOA.minimum
= bin.unpack(">I5", data, np)
end
-- An iterator that returns the positions of nonzero bits in the given binary
-- string.
local function bit_iter(bits)
return coroutine.wrap(function()
for i = 1, #bits do
local n = string.byte(bits, i)
local j = 0
local mask = 0x80
while mask > 0 do
if bit.band(n, mask) ~= 0 then
coroutine.yield((i - 1) * 8 + j)
end
j = j + 1
mask = bit.rshift(mask, 1)
end
end
end)
end
-- Decodes NSEC records, puts result in <code>entry.NSEC</code>. See RFC 4034,
-- section 4.
--
-- <code>entry.NSEC</code> has the fields <code>dname</code>,
-- <code>next_dname</code>, and <code>types</code>.
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.NSEC] = function (entry, data, pos)
local np = pos - #entry.data
entry.NSEC = {}
entry.NSEC.dname = entry.dname
np, entry.NSEC.next_dname = decStr(data, np)
while np < pos do
local block_num, type_bitmap
np, block_num, type_bitmap = bin.unpack(">Cp", data, np)
entry.NSEC.types = {}
for i in bit_iter(type_bitmap) do
entry.NSEC.types[(block_num - 1) * 256 + i] = true
end
end
end
-- Decodes records that consist only of one domain, for example CNAME, NS, PTR.
-- Puts result in <code>entry.domain</code>.
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
local function decDomain(entry, data, pos)
local np = pos - #entry.data
local _
_, entry.domain = decStr(data, np)
end
-- Decodes CNAME records.
-- Puts result in <code>entry.domain</code>.
-- @name decoder[types.CNAME]
-- @class function
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.CNAME] = decDomain
-- Decodes NS records.
-- Puts result in <code>entry.domain</code>.
-- @name decoder[types.NS]
-- @class function
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.NS] = decDomain
-- Decodes PTR records.
-- Puts result in <code>entry.domain</code>.
-- @name decoder[types.PTR]
-- @class function
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.PTR] = decDomain
-- Decodes TXT records.
-- Puts result in <code>entry.domain</code>.
-- @name decoder[types.TXT]
-- @class function
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.TXT] =
function (entry, data, pos)
local len = entry.data:len()
local np = pos - #entry.data
local txt_len
local txt
if len > 0 then
entry.TXT = {}
entry.TXT.text = {}
end
while len > 0 do
np, txt_len = bin.unpack("C", data, np)
np, txt = bin.unpack("A" .. txt_len, data, np )
len = len - txt_len - 1
table.insert( entry.TXT.text, txt )
end
end
---
-- Decodes OPT record, puts it in <code>entry.OPT</code>.
--
-- <code>entry.OPT</code> has the fields <code>mname</code>, <code>rname</code>,
-- <code>serial</code>, <code>refresh</code>, <code>retry</code>,
-- <code>expire</code>, and <code>minimum</code>.
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.OPT] =
function(entry, data, pos)
local np = pos - #entry.data - 6
local opt = { bufsize = entry.class }
np, opt.rcode, opt.version, opt.zflags, opt.rdlen = bin.unpack(">CCSS", data, np)
np, opt.data = bin.unpack("A" .. opt.rdlen, data, np)
entry.OPT = opt
end
-- Decodes MX record, puts it in <code>entry.MX</code>.
--
-- <code>entry.MX</code> has the fields <code>pref</code> and
-- <code>server</code>.
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.MX] =
function(entry, data, pos)
local np = pos - #entry.data + 2
local _
entry.MX = {}
_, entry.MX.pref = bin.unpack(">S", entry.data)
_, entry.MX.server = decStr(data, np)
end
-- Decodes SRV record, puts it in <code>entry.SRV</code>.
--
-- <code>entry.SRV</code> has the fields <code>prio</code>,
-- <code>weight</code>, <code>port</code> and
-- <code>target</code>.
-- @param entry RR in packet.
-- @param data Complete encoded DNS packet.
-- @param pos Position in packet after RR.
decoder[types.SRV] =
function(entry, data, pos)
local np = pos - #entry.data
local _
entry.SRV = {}
np, entry.SRV.prio, entry.SRV.weight, entry.SRV.port = bin.unpack(">S>S>S", data, np)
np, entry.SRV.target = decStr(data, np)
end
-- Decodes returned resource records (answer, authority, or additional part).
-- @param data Complete encoded DNS packet.
-- @param count Value of according counter in header.
-- @param pos Starting position in packet.
-- @return Table of RRs.
local function decodeRR(data, count, pos)
local ans = {}
for i = 1, count do
local currRR = {}
pos, currRR.dname = decStr(data, pos)
pos, currRR.dtype, currRR.class, currRR.ttl = bin.unpack(">SSI", data, pos)
local reslen
pos, reslen = bin.unpack(">S", data, pos)
pos, currRR.data = bin.unpack("A" .. reslen, data, pos)
-- try to be smart: decode per type
if decoder[currRR.dtype] then
decoder[currRR.dtype](currRR, data, pos)
end
table.insert(ans, currRR)
end
return pos, ans
end
---
-- Splits a string up into a table of single characters.
-- @param str String to be split up.
-- @return Table of characters.
local function str2tbl(str)
local tbl = {}
for i = 1, #str do
table.insert(tbl, string.sub(str, i, i))
end
return tbl
end
---
-- Decodes DNS flags.
-- @param flgStr Flags as a binary digit string.
-- @return Table representing flags.
local function decodeFlags(flgStr)
local flags = {}
local flgTbl = str2tbl(flgStr)
if flgTbl[1] == '1' then flags.QR = true end
if flgTbl[2] == '1' then flags.OC1 = true end
if flgTbl[3] == '1' then flags.OC2 = true end
if flgTbl[4] == '1' then flags.OC3 = true end
if flgTbl[5] == '1' then flags.OC4 = true end
if flgTbl[6] == '1' then flags.AA = true end
if flgTbl[7] == '1' then flags.TC = true end
if flgTbl[8] == '1' then flags.RD = true end
if flgTbl[9] == '1' then flags.RA = true end
if flgTbl[13] == '1' then flags.RC1 = true end
if flgTbl[14] == '1' then flags.RC2 = true end
if flgTbl[15] == '1' then flags.RC3 = true end
if flgTbl[16] == '1' then flags.RC4 = true end
return flags
end
---
-- Decodes a DNS packet.
-- @param data Encoded DNS packet.
-- @return Table representing DNS packet.
function decode(data)
local pos
local pkt = {}
local encFlags
local cnt = {}
pos, pkt.id, encFlags, cnt.q, cnt.a, cnt.auth, cnt.add = bin.unpack(">SB2S4", data)
-- for now, don't decode the flags
pkt.flags = decodeFlags(encFlags)
--
-- check whether this is an update response or not
-- a quick fix to allow decoding of non updates and not break for updates
-- the flags are enough for the current code to determine whether an update was successful or not
--
local strflags=encodeFlags(pkt.flags)
if ( strflags:sub(1,4) == "1010" ) then
return pkt
else
pos, pkt.questions = decodeQuestions(data, cnt.q, pos)
pos, pkt.answers = decodeRR(data, cnt.a, pos)
pos, pkt.auth = decodeRR(data, cnt.auth, pos)
pos, pkt.add = decodeRR(data, cnt.add, pos)
end
return pkt
end
---
-- Creates a new table representing a DNS packet.
-- @return Table representing a DNS packet.
function newPacket()
local pkt = {}
pkt.id = 1
pkt.flags = {}
pkt.flags.RD = true
pkt.questions = {}
pkt.zones = {}
pkt.updates = {}
pkt.answers = {}
pkt.auth = {}
pkt.additional = {}
return pkt
end
---
-- Adds a question to a DNS packet table.
-- @param pkt Table representing DNS packet.
-- @param dname Domain name to be asked.
-- @param dtype RR to be asked.
function addQuestion(pkt, dname, dtype, class)
if type(pkt) ~= "table" then return nil end
if type(pkt.questions) ~= "table" then return nil end
local class = class or CLASS.IN
local q = {}
q.dname = dname
q.dtype = dtype
q.class = class
table.insert(pkt.questions, q)
return pkt
end
get_default_timeout = function()
local timeout = {[0] = 10000, 7000, 5000, 4000, 4000, 4000}
return timeout[nmap.timing_level()] or 4000
end
---
-- Adds a zone to a DNS packet table
-- @param pkt Table representing DNS packet.
-- @param dname Domain name to be asked.
function addZone(pkt, dname)
if ( type(pkt) ~= "table" ) or (type(pkt.updates) ~= "table") then return nil end
table.insert(pkt.zones, { dname=dname, dtype=types.SOA, class=CLASS.IN })
return pkt
end
---
-- Encodes the Z bitfield of an OPT record.
-- @param flags Flag table, each entry representing a flag (only DO flag implmented).
-- @return Binary digit string representing flags.
local function encodeOPT_Z(flags)
if type(flags) == "string" then return flags end
if type(flags) ~= "table" then return nil end
local bits = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
for n, k in pairs({[1] = "DO"}) do
if flags[k] then
bits[n] = 1
end
end
return table.concat(bits)
end
---
-- Adds an client-subnet paylod to the OPT packet
-- implementing http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-00
-- @param pkt Table representing DNS packet.
-- @param Z Table of Z flags. Only DO is supported.
function add_client_subnet (pkt,Z,client_subnet)
local udp_payload_size = 4096
local code = 20730 -- temporay option-code http://comments.gmane.org/gmane.ietf.dnsext/19776
if not client_subnet.family then
client_subnet.family = 1 -- ipv4
end
local scope_mask = 0 -- In requests, it MUST be set to 0 see draft
-- local addr = stdnse.strsplit("%.",client_subnet.address)
-- local data = bin.pack(">SCCCCCC",client_subnet.family,client_subnet.mask,scope_mask,tonumber(addr[1]),tonumber(addr[2]),tonumber(addr[3]),tonumber(addr[4]))
local data = bin.pack(">SCCI",client_subnet.family,client_subnet.mask,scope_mask,client_subnet.address)
local len = #data
local opt = bin.pack(">SS",code, #data) .. data
addOPT(pkt,Z,opt)
end
---
-- Adds an NSID paylod to the OPT packet
-- @param pkt Table representing DNS packet.
-- @param Z Table of Z flags. Only DO is supported.
function addNSID (pkt,Z)
local udp_payload_size = 4096
local opt = bin.pack(">SS",3, 0) -- nsid data
addOPT(pkt,Z,opt)
end
---
-- Adds an OPT RR to a DNS packet's additional section. Only the table of Z
-- flags is supported (i.e., not RDATA). See RFC 2671 section 4.3.
-- @param pkt Table representing DNS packet.
-- @param Z Table of Z flags. Only DO is supported.
function addOPT(pkt, Z, opt)
local rdata = opt or ""
if type(pkt) ~= "table" then return nil end
if type(pkt.additional) ~= "table" then return nil end
local _, Z_int = bin.unpack(">S", bin.pack("B", encodeOPT_Z(Z)))
local opt = {
type = types.OPT,
class = 4096, -- Actually the sender UDP payload size.
ttl = 0 * (0x01000000) + 0 * (0x00010000) + Z_int,
rdlen = #rdata,
rdata = rdata,
}
table.insert(pkt.additional, opt)
return pkt
end
---
-- Adds a update to a DNS packet table
-- @param pkt Table representing DNS packet.
-- @param dname Domain name to be asked.
-- @param dtype to be updated
-- @param ttl the time-to-live of the record
-- @param data type specific data
function addUpdate(pkt, dname, dtype, ttl, data, class)
if ( type(pkt) ~= "table" ) or (type(pkt.updates) ~= "table") then return nil end
table.insert(pkt.updates, { dname=dname, dtype=dtype, class=class, ttl=ttl, data=(data or "") } )
return pkt
end
--- Adds a record to the Zone
-- @param dname containing the hostname to add
-- @param options A table containing any of the following fields:
-- * <code>dtype</code>: Desired DNS record type (default: <code>"A"</code>).
-- * <code>host</code>: DNS server to be queried (default: DNS servers known to Nmap).
-- * <code>timeout</code>: The time to wait for a response
-- * <code>sendCount</code>: The number of send attempts to perform
-- * <code>zone</code>: If not supplied deduced from hostname
-- * <code>data</code>: Table or string containing update data (depending on record type):
-- A - String containing the IP address
-- CNAME - String containing the FQDN
-- MX - Table containing <code>pref</code>, <code>mx</code>
-- SRV - Table containing <code>prio</code>, <code>weight</code>, <code>port</code>, <code>target</code>
--
-- @return status true on success false on failure
-- @return msg containing the error message
--
-- Examples
--
-- Adding different types of records to a server
-- * update( "www.cqure.net", { host=host, port=port, dtype="A", data="10.10.10.10" } )
-- * update( "alias.cqure.net", { host=host, port=port, dtype="CNAME", data="www.cqure.net" } )
-- * update( "cqure.net", { host=host, port=port, dtype="MX", data={ pref=10, mx="mail.cqure.net"} })
-- * update( "_ldap._tcp.cqure.net", { host=host, port=port, dtype="SRV", data={ prio=0, weight=100, port=389, target="ldap.cqure.net" } } )
--
-- Removing the above records by setting an empty data and a ttl of zero
-- * update( "www.cqure.net", { host=host, port=port, dtype="A", data="", ttl=0 } )
-- * update( "alias.cqure.net", { host=host, port=port, dtype="CNAME", data="", ttl=0 } )
-- * update( "cqure.net", { host=host, port=port, dtype="MX", data="", ttl=0 } )
-- * update( "_ldap._tcp.cqure.net", { host=host, port=port, dtype="SRV", data="", ttl=0 } )
--
function update(dname, options)
local options = options or {}
local pkt = newPacket()
local flags = pkt.flags
local host, port = options.host, options.port
local timeout = ( type(options.timeout) == "number" ) and options.timeout or get_default_timeout()
local sendcount = options.sendCount or 2
local dtype = ( type(options.dtype) == "string" ) and types[options.dtype] or types.A
local updata = options.data
local ttl = options.ttl or 86400
local zone = options.zone or dname:match("^.-%.(.+)$")
local class = CLASS.IN
assert(host, "dns.update needs a valid host in options")
assert(port, "dns.update needs a valid port in options")
if ( options.zone ) then dname = dname .. "." .. options.zone end
if ( not(zone) and not( dname:match("^.-%..+") ) ) then
return false, "hostname needs to be supplied as FQDN"
end
flags.RD = false
flags.OC1, flags.OC2, flags.OC3, flags.OC4 = false, true, false, true
-- If ttl is zero and updata is string and zero length or nil, assume delete record
if ( ttl == 0 and ( ( type(updata) == "string" and #updata == 0 ) or not(updata) ) ) then
class = CLASS.ANY
updata = ""
if ( types.MX == dtype and not(options.zone) ) then zone=dname end
if ( types.SRV == dtype and not(options.zone) ) then
zone=dname:match("^_.-%._.-%.(.+)$")
end
-- if not, let's try to update the zone
else
if ( dtype == types.A ) then
updata = updata and bin.pack(">I", ipOps.todword(updata)) or ""
elseif( dtype == types.CNAME ) then
updata = encodeFQDN(updata)
elseif( dtype == types.MX ) then
assert( not( type(updata) ~= "table" ), "dns.update expected options.data to be a table")
if ( not(options.zone) ) then zone = dname end
local data = bin.pack(">S", updata.pref)
data = data .. encodeFQDN(updata.mx)
updata = data
elseif ( dtype == types.SRV ) then
assert( not( type(updata) ~= "table" ), "dns.update expected options.data to be a table")
local data = bin.pack(">SSS", updata.prio, updata.weight, updata.port )
data = data .. encodeFQDN(updata.target)
updata = data
zone = options.zone or dname:match("^_.-%._.-%.(.+)$")
else
return false, "Unsupported record type"
end
end
pkt = addZone(pkt, zone)
pkt = addUpdate(pkt, dname, dtype, ttl, updata, class)
local data = encode(pkt)
local status, response = sendPackets(data, host, port, timeout, sendcount, false)
if ( status ) then
local decoded = decode(response[1].data)
local flags=encodeFlags(decoded.flags)
if (flags:sub(-4) == "0000") then
return true
end
end
return false
end
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