local bit = require "bit" 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 -- @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 http://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 (bit.band(string.byte(result,3), 0x80) == 0x80 and bit.band(string.byte(result,4), 0x85) == 0x80) then return "Recursion appears to be enabled" end return end