/usr/share/nmap/scripts/dns-recursion.nse is in nmap 5.21-1.1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | 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.
]]
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
-- 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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