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.
]]
---
-- @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", "intrusive"}
require "bit"
require "comm"
require "shortport"
portrule = shortport.portnumber(53, "udp")
action = function(host, port)
-- generate dns query, Transaction-ID 0xdead, www.wikipedia.org (type A, class IN)
local request = string.char(0xde, 0xad, 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03) .. "www" .. string.char(0x09) .. "wikipedia" .. string.char(0x03) .. "org" .. string.char(0x00, 0x00, 0x01, 0x00, 0x01)
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
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