description = [[ Performs DNS cache snooping against a DNS server. There are two modes of operation, controlled by the dns-cache-snoop.mode script argument. In nonrecursive mode (the default), queries are sent to the server with the RD (recursion desired) flag set to 0. The server should respond positively to these only if it has the domain cached. In timed mode, the mean and standard deviation response times for a cached domain are calculated by sampling the resolution of a name (www.google.com) several times. Then, each domain is resolved and the time taken compared to the mean. If it is less than one standard deviation over the mean, it is considered cached. The timed mode inserts entries in the cache and can only be used reliably once. The default list of domains to check consists of the top 50 most popular sites, each site being listed twice, once with "www." and once without. Use the dns-cache-snoop.domains script argument to use a different list. ]] --- -- @args dns-cache-snoop.mode which of two supported snooping methods to -- use. nonrecursive, the default, checks if the server -- returns results for non-recursive queries. Some servers may disable -- this. timed measures the difference in time taken to -- resolve cached and non-cached hosts. This mode will pollute the DNS -- cache and can only be used once reliably. -- @args dns-cache-snoop.domains an array of domain to check in place of -- the default list. -- -- @usage -- nmap -sU -p 53 --script dns-cache-snoop.nse --script-args 'dns-cache-snoop.mode=timed,dns-cache-snoop.domains={host1,host2,host3}' -- -- @output -- PORT STATE SERVICE REASON -- 53/udp open domain udp-response -- | dns-cache-snoop: 10 of 100 tested domains are cached. -- | www.google.com -- | facebook.com -- | www.facebook.com -- | www.youtube.com -- | yahoo.com -- | twitter.com -- | www.twitter.com -- | www.google.com.hk -- | www.google.co.uk -- |_www.linkedin.com 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" categories = {"intrusive", "discovery"} portrule = shortport.port_or_service(53, "domain", "udp") local DOMAINS = {} local MODE = "nonrecursive" -- This domain is used as a default cached entry in timed mode. local TIMED_DUMMY_DOMAIN = "www.google.com" -- How many samples to collect for the time taken to resolve the dummy domain. local TIMED_NUM_SAMPLES = 25 -- In timed mode, times below mean + TIMED_MULTIPLIER * stddev are -- accepted as cached. Using one standard deviation gives us a roughly -- 84% chance that a domain with the same response time as the reference -- domain will be detected as cached. local TIMED_MULTIPLIER = 1.0 -- This list is the first 50 entries of -- http://s3.amazonaws.com/alexa-static/top-1m.csv.zip on 2010-06-11. local ALEXA_DOMAINS = { "google.com", "facebook.com", "youtube.com", "yahoo.com", "live.com", "wikipedia.org", "baidu.com", "blogger.com", "msn.com", "qq.com", "twitter.com", "yahoo.co.jp", "google.co.in", "taobao.com", "google.de", "google.com.hk", "wordpress.com", "amazon.com", "sina.com.cn", "google.co.uk", "microsoft.com", "bing.com", "google.fr", "ebay.com", "myspace.com", "yandex.ru", "google.co.jp", "linkedin.com", "163.com", "google.com.br", "mail.ru", "flickr.com", "craigslist.org", "google.it", "fc2.com", "conduit.com", "rapidshare.com", "vkontakte.ru", "google.es", "googleusercontent.com", "bbc.co.uk", "imdb.com", "soso.com", "doubleclick.com", "go.com", "livejasmin.com", "apple.com", "aol.com", "bp.blogspot.com", "youku.com", } -- Construct the default list of domains. for _, domain in ipairs(ALEXA_DOMAINS) do DOMAINS[#DOMAINS + 1] = domain if not string.match(domain, "^www\.") then DOMAINS[#DOMAINS + 1] = "www." .. domain end end -- Return the mean and sample standard deviation of an array, using the -- algorithm from Knuth Vol. 2, Section 4.2.2. function mean_stddev(t) local i, m, s, sigma if #t == 0 then return 0, nil end m = t[1] s = 0 for i = 2, #t do local mp = m m = m + (t[i] - m) / i s = s + (t[i] - mp) * (t[i] - m) end sigma = math.sqrt(s / (#t - 1)) return m, sigma end local function nonrecursive_mode(host, port, domains) local cached = {} for _,domain in ipairs(domains) do if dns.query(domain, {host = host.ip, port = port.number, tries = 0, norecurse=true}) then cached[#cached + 1] = domain end end return cached end -- Return the time taken (in seconds) to resolve the given domain, or nil if -- it could not be resolved. local function timed_query(host, port, domain) local start, stop start = nmap.clock_ms() if dns.query(domain, {host = host.ip, port = port.number, tries = 0, norecurse = false}) then stop = nmap.clock_ms() return (stop - start) / 1000 else return nil end end local function timed_mode(host, port, domains) local cached = {} local i, t -- Insert in the cache. timed_query(host, port, TIMED_DUMMY_DOMAIN) -- Measure how long it takes to resolve on average. local times = {} local mean, stddev local cutoff for i = 1, TIMED_NUM_SAMPLES do t = timed_query(host, port, TIMED_DUMMY_DOMAIN) if t then times[#times + 1] = t end end mean, stddev = mean_stddev(times) cutoff = mean + stddev * TIMED_MULTIPLIER stdnse.print_debug(1, "dns-cache-snoop: reference %s: mean %g stddev %g cutoff %g", TIMED_DUMMY_DOMAIN, mean, stddev, cutoff) -- Now try all domains one by one. for _, domain in ipairs(domains) do t = timed_query(host, port, domain) if t then if t < cutoff then stdnse.print_debug(1, "dns-cache-snoop: %s: %g is cached (cutoff %g)", domain, t, cutoff) cached[#cached + 1] = domain else stdnse.print_debug(1, "dns-cache-snoop: %s: %g not cached (cutoff %g)", domain, t, cutoff) end end end return cached end action = function(host, port) local domains = DOMAINS local mode = MODE local args = nmap.registry.args if args then if args["dns-cache-snoop.mode"] then mode = args["dns-cache-snoop.mode"] end if args["dns-cache-snoop.domains"] then domains = args["dns-cache-snoop.domains"] end end local cached mode = string.lower(mode) if mode == "nonrecursive" then cached = nonrecursive_mode(host, port, domains) elseif mode == "timed" then cached = timed_mode(host, port, domains) else return string.format("Error: \"%s\" is not a known mode. Use \"nonrecursive\" or \"timed\".") end if #cached > 0 then nmap.set_port_state(host, port, "open") end return string.format("%d of %d tested domains are cached.\n", #cached, #domains) .. stdnse.strjoin("\n", cached) end