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local comm = require "comm"
local nmap = require "nmap"
local shortport = require "shortport"
local string = require "string"
description = [[
Checks if a DNS server allows queries for third-party names. It is
expected that recursion will be enabled on your own internal
nameservers.
]]
---
-- @usage
-- nmap -sU -p 53 --script=dns-recursion <target>
-- @output
-- PORT STATE SERVICE REASON
-- 53/udp open domain udp-response
-- |_dns-recursion: Recursion appears to be enabled
author = "Felix Groebert"
license = "Same as Nmap--See https://nmap.org/book/man-legal.html"
categories = {"default", "safe"}
portrule = shortport.portnumber(53, "udp")
action = function(host, port)
-- generate dns query
local request = "\xde\xad" -- Transaction-ID 0xdead
.. "\x01\x00" -- flags (recursion desired)
.. "\x00\x01" -- 1 question
.. "\x00\x00" -- 0 answers
.. "\x00\x00" -- 0 authority
.. "\x00\x00" -- 0 additional
.. "\x03www\x09wikipedia\x03org\x00" -- www.wikipedia.org.
.. "\x00\x01" -- type A
.. "\x00\x01" -- class IN
local status, result = comm.exchange(host, port, request, {proto="udp"})
if not status then
return
end
nmap.set_port_state(host, port, "open")
-- parse response for dns flags
if (string.byte(result,3) & 0x80) == 0x80
and (string.byte(result,4) & 0x85) == 0x80
then
return "Recursion appears to be enabled"
end
return
end
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