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40f36a4e3e
Changes fall into these categories: 1. Avoid pathological string building. Loops over x = x .. "foo" can become very slow. Instead, use strbuf.lua, table.concat, or just one continuous concatenation; a = x .. y .. z is one operation, better than a = x .. y; a = a .. z 2. Use hex-escaped strings instead of string.char. I find this more readable in many cases, and it avoids a table lookup and function call. 3. Don't duplicate code. A few libraries and scripts had re-implemented stdnse.generate_random_string or openssl.rand_bytes.
60 lines
1.5 KiB
Lua
60 lines
1.5 KiB
Lua
local bit = require "bit"
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local comm = require "comm"
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local nmap = require "nmap"
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local shortport = require "shortport"
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local string = require "string"
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description = [[
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Checks if a DNS server allows queries for third-party names. It is
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expected that recursion will be enabled on your own internal
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nameservers.
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]]
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---
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-- @usage
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-- nmap -sU -p 53 --script=dns-recursion <target>
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-- @output
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-- PORT STATE SERVICE REASON
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-- 53/udp open domain udp-response
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-- |_dns-recursion: Recursion appears to be enabled
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author = "Felix Groebert"
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license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
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categories = {"default", "safe"}
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portrule = shortport.portnumber(53, "udp")
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action = function(host, port)
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-- generate dns query
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local request = "\xde\xad" -- Transaction-ID 0xdead
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.. "\x01\x00" -- flags (recursion desired)
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.. "\x00\x01" -- 1 question
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.. "\x00\x00" -- 0 answers
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.. "\x00\x00" -- 0 authority
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.. "\x00\x00" -- 0 additional
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.. "\x03www\x09wikipedia\x03org\x00" -- www.wikipedia.org.
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.. "\x00\x01" -- type A
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.. "\x00\x01" -- class IN
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local status, result = comm.exchange(host, port, request, {proto="udp"})
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if not status then
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return
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end
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nmap.set_port_state(host, port, "open")
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-- parse response for dns flags
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if (bit.band(string.byte(result,3), 0x80) == 0x80
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and bit.band(string.byte(result,4), 0x85) == 0x80)
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then
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return "Recursion appears to be enabled"
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end
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return
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end
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