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Re: DNS cache snooping script

From: Ron <ron () skullsecurity net>
Date: Mon, 12 Apr 2010 13:55:42 -0500
For what it's worth, I tested the script against a bunch of different DNS servers, and it worked as advertised. I'm 
pretty sure none of the servers lied in their responses, though. 

Am I crazy, or did you copy/paste the script straight into your email? Can you send it as an attachment instead? I had 
to fix a bunch of formatting before I could run it. 

Thanks!

On Mon, 12 Apr 2010 10:50:29 -0600 Eugene Alexeev
<eugene.alexeev () gmail com> wrote:

Ron,

Thanks!  I'm glad you like the script.  I based the default list on
the the thought: "If I was doing a pen test against someone, what
would I like to know?".  The answer I came up with for this question
was:
1.  If I have to do social engineering, where can I find the
employees?
2.  What operating systems are present in the environment, even if
they are not visible during the nmap scan?
3.  [How] do they patch and how frequently?
4.  How would I detect that the DNS server is lying to me?

So based on that, I stuck in:  common social sites, email login pages,
operating system pages, some update pages, and some obscure pages
(like kernel.org and insecure.org).  I've also built in the ability
for the user to supply their own queries via --script-args
snoop_hosts={host0\,host1\,hostN}.

I have not looked into multiple host names per query, but I will
investigate it.

Timed mode takes the longest because the script does 25 look ups on
www.google.com once it's been cached to profile how long a cached
query takes.  I've not benchmarked the script, but the default
configuration appears to perform reasonably (~ under 15 seconds).  My
unofficial observations are that cached queries take between 10-130ms
on average and non-cached queries can take as long as 4 seconds.  So,
it all depends on you patient you can afford to be!

Eugene


On Mon, Apr 12, 2010 at 10:33 AM, Ron <ron () skullsecurity net> wrote:


Hey Eugene,

That script looks really cool! I was thinking of writing something
similar, but you saved me the trouble.

Out of curiosity, where did you get the list of domains you look
for, or is it simply arbitrary? I'm trying to think of which
domains would be the most interesting - maybe others will have some
better input than me. My first thought is those used by automatic
updaters (java update, oracle, windows, etc), those used by
different Linux distributions, and those used by known malware. All
of them could be interesting when testing a network. I was thinking
of the top-xxx sites from some service (Alexa, I think?), but I
don't think that'd give you anything interesting.

How long does it take to look up the different domains? Are/can you
look up more than one hostname per DNS request to speed it up? How
many domains can be realistically checked in a single query? Tens,
hundreds, thousands?


On Mon, 12 Apr 2010 10:18:23 -0600 Eugene Alexeev
<eugene.alexeev () gmail com> wrote:

All,

I'm submitting the following NSE script for your scrutiny.  Please
note that it may error out with versions that do not include the
fix to dns.lua that was addressed by svn revision 17270.


description = [[
Performs DNS cache snooping against a DNS server.

This script has two modes of operation: non-recursive (used by
default) and timed.  The default mode makes DNS type A queries to
the dns server with the

Recursion Desired (RD) flag set to 0 and tries set to 0.  Any
successful queries
are assumed to come from the server's cache.  The timed mode uses
temporal analysis to deterime where or not each host is in the
server's cache. First,
it sends a recursive DNS query for www.google.com to the server.
This ensures
that the response for www.google.com has been cached. It then
makes recursive
requests for each host in the list and records their timing
information. Then
the mean cached query time is calculated along with cached query
time sigma.

Each host's timing data is then evaluated, if the query tooklonger
than cached
mean + ( cached sigma * multiplier), then the response is
considered not to have
been cached.

Please note that the timed mode will pollute the DNS server's
cache. ]]

---
-- @param snoop_mode timed: use the timed mode rather than the
default
--                          non-recursive mode.
-- @param snoop_multiplier x.x: can be used to adjust the
maxDeviation parameter
--                          used in timed mode.
-- @param snoop_hosts {host0,host1,hostN}: check if the supplied
hosts are
--                          in the DNS cache rather than querying
using default
--                          snoop_hosts table.
--
-- @output
-- 53/udp open|filtered domain
-- | dns-cache-snoop: DNS cache contains:
-- | -->    login.yahoo.com
-- | -->    mail.aol.com
-- | -->    my.screenname.aol.com
-- | -->    gmx.com
-- | -->    hotmail.com
-- | -->    login.live.com
-- | -->    www.facebook.com
-- | -->    facebook.com
-- | -->    www.twitter.com
-- | -->    twitter.com
-- | -->    www.linkedin.com
-- |_-->    linkedin.com
--
-- @usage
-- nmap --script dns-cache-snoop.nse \
--      --script-args snoop_mode=timed,
--                    snoop_multiplier=x.x,
--                    snoop_hosts={host0\,host1\,hostN}

require('shortport')
require('dns')
require('stdnse')
require('nmap')
require('math')

author = "Eugene V. Alexeev"

license = 'Same as Nmap--See http://nmap.org/book/man-legal.html&apos;

categories = {'default', 'intrusive', 'discovery'}

portrule = shortport.portnumber(53, 'udp')


--- Default list of hosts to check
--@class table
--@name snoop_hosts
local snoop_hosts = {
    'mail.google.com', 'gmail.com',                 --- Gmail
    'mail.yahoo.com', 'login.yahoo.com',            --- Yahoo Mail
    'mail.aol.com', 'my.screenname.aol.com',        --- AOL/AIM
Mail 'www.gmx.com', 'gmx.com',                       --- GMX Mail
    'hotmail.com', 'login.live.com',                --- Hotmail /
MSN Live 'www.facebook.com', 'facebook.com',             ---
Facebook 'www.twitter.com', 'twitter.com',               ---
Twitter 'www.linkedin.com', 'linkedin.com',             ---
LinkedIn 'www.plaxo.com', 'plaxo.com',                   --- Plaxo
    'www.myspace.com', 'myspace.com',               --- MySpace
    'www.ivillage.com', 'ivillage.com',             --- iVillage
    'www.flickr.com', 'flickr.com',                 --- Flickr
    'www.youtube.com', 'youtube.com',               --- Youtube
    'www.digg.com', 'digg.com',                     --- Digg
    'www.reddit.com', 'reddit.com',                 --- Reddit
    'www.craigslist.com', 'craigslist.com',         --- Craigslist
    'update.microsoft.com',                         --- MS Patches
    'www.microsoft.com', 'microsoft.com',           --- General MS
    'technet.microsoft.com',                        --- Technet
Access 'rhn.com','rhn.redhat.com','redhat.com',        --- RHN
Access 'www.novell.com', 'novell.com',                 --- SLES /
SLED 'www.kernel.org', 'kernel.org',                 --- Kernel
Sources, etc 'www.ubuntu.com', 'ubuntu.com',                 ---
Ubuntu 'www.debian.com', 'debian.com',                 --- Debian
    'www.freebsd.org', 'freebsd.org',               --- FreeBSD
    'www.openbsd.org', 'openbsd.org',               --- OpenBSD
    'www.oracle.com', 'oracle.com',                 --- Oracle
    'docs.sun.com', 'www.sun.com', 'sun.com',       ---
Sun/Solaris Docs 'www.centos.org', 'centos.org',
--- CentOS 'www.nmap.org', 'nmap.org',                     ---
Couldn't Resist 'ha.ckers.org', 'sla.ckers.org'
--- Should not be present
                                                    --- in most
caches! }


--- Default snoop_multiplier, used to control the maxDeviation
paramter in
--  timed mode, has no meaning in non-recursive mode.
--  @class number
--  @name snoop_multiplier
local snoop_multiplier = 1.0


--- Function to determine the standard deviation of a table
--  @class function
--  @name standardDeviation
--  @param t table containing numeric values
--- @return sigma for values in table t
--  THIS FUNCTION WAS NOT WRITTED BY ME, FULL CREDIT GOES TO THE
AUTHOR OF:
--  http://lua-users.org/wiki/SimpleStats
function standardDeviation( t )
  local m
  local vm
  local sum = 0
  local count = 0
  local result

  m = mean( t )

  for k,v in pairs(t) do
    if type(v) == 'number' then
      vm = v - m
      sum = sum + (vm * vm)
      count = count + 1
    end
  end

  result = math.sqrt(sum / (count-1))

  return result
end


--- Function to determine the mean value of a table
--  @class function
--  @name mean
--  @param t table containing numeric values
--  @return the mean for values in table t
--  THIS FUNCTION WAS NOT WRITTED BY ME, FULL CREDIT GOES TO THE
AUTHOR OF:
--  http://lua-users.org/wiki/SimpleStats
function mean( t )
  local sum = 0
  local count= 0

  for k,v in pairs(t) do
    if type(v) == 'number' then
      sum = sum + v
      count = count + 1
    end
  end

  return (sum / count)
end


--- Wrapper for nselib/dns.query function, performs non-recursive
DNS queries
--  @class function
--  @name nr_query
--  @param hostname hostname to look up
--  @param host host table provided by NSE
--  @param port port table provided by NSE
--  @return true if an answer is received
--  @return false if no answer is recevied
function nr_query(hostname, host, port)
  local q = dns.query(hostname,             -- Host name to query
for {host=host.ip,         -- IP of DNS server
                      port=port.number,     -- Port of DNS server
                      tries = 0,            -- Do not query other
servers norecurse=true})      -- Perform a non-recursive query
  if q then
    return true

else

    return false
  end
end


--- Function to calculate the time (ms) it took to perform a
specific recursive
--  DNS query.
--  @class function
--  @name timed_query
--  @param hostname hostname to look up
--  @param host host table provided by NSE
--  @param port port table provided by NSE
--  @return response time in ms
--  @return -1 if an error occured
function timed_query(hostname, host, port)
  local start = nmap.clock_ms()

  local q = dns.query(hostname,             -- Host name to query
for {host=host.ip,         -- IP of DNS server
                      port=port.number,     -- Port of DNS server
                      tries=0,              -- Do not query other
servers norecurse=false})     -- Perform a recursive query

  local stop = nmap.clock_ms()

  if q then
    return (stop - start)
  else
    return -1
  end
end


action = function(host, port)
  local inCache = {}

  if nmap.registry.args.snoop_hosts ~= nil then
    stdnse.print_debug("Will snoop for %d custom hosts",
                       #nmap.registry.args.snoop_hosts)
    snoop_hosts = nmap.registry.args.snoop_hosts
  end

  --- Timed mode
  if nmap.registry.args.snoop_mode ~= nil and
     nmap.registry.args.snoop_mode == "timed" then
     stdnse.print_debug("Using timed mode.")

    if nmap.registry.args.snoop_multiplier ~= nil then
      stdnse.print_debug("Setting snoop_multiplier to %f",
                         nmap.registry.args.snoop_multiplier)

      snoop_multiplier = nmap.registry.args.snoop_multiplier
    end

    timed_query('www.google.com', host, port)

    local cachedTimes = {}

    for i=1,25 do
      local ms = timed_query('www.google.com', host, port)
      if ms > 0 then
        table.insert(cachedTimes, ms)
      end
    end

    local queryTimes = {}

    for i,hostname in ipairs(snoop_hosts) do
      local ms = timed_query(hostname, host, port)
      if ms > 0 then
        queryTimes[hostname] = ms
      end
    end

    local cachedMean = mean(cachedTimes)
    local cachedSigma = standardDeviation(cachedTimes)
    local maxDeviation = cachedSigma * snoop_multiplier
    local maxCachedTime = cachedMean + maxDeviation

    stdnse.print_debug("Mean cached response time: %f ms",
cachedMean) stdnse.print_debug("Cached response time sigma: %f
ms", cachedSigma) stdnse.print_debug("Max Deviation: %f ms",
maxDeviation)

    for hostname, response_time in pairs(queryTimes) do
      stdnse.print_debug("%s : %f", hostname, response_time)
      if response_time > 0 and response_time <= maxCachedTime then
        table.insert(inCache, hostname)
      end
    end

  --- Non-recursive mode
  else
    for i,hostname in ipairs(snoop_hosts) do
      if nr_query(hostname, host, port) then
        table.insert(inCache, hostname)
      end
    end
  end

  --- Organize and return the results
  local resultString = "DNS cache contains:\n"

  for i,hostname in ipairs(inCache) do
    resultString =  resultString .. "-->\t" .. hostname .. "\n"
  end

  if # resultString > 20 then return resultString else return end
end


Thanks for your time & looking forward to your feedback.

Eugene
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--
Ron Bowes
http://www.skullsecurity.org
http://www.twitter.com/iagox86

_______________________________________________
Sent through the nmap-dev mailing list
http://cgi.insecure.org/mailman/listinfo/nmap-dev
Archived at http://seclists.org/nmap-dev/


_______________________________________________
Sent through the nmap-dev mailing list
http://cgi.insecure.org/mailman/listinfo/nmap-dev
Archived at http://seclists.org/nmap-dev/



-- 
Ron Bowes
http://www.skullsecurity.org
http://www.twitter.com/iagox86

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