description = [[ Attempts to relay mail by issuing a predefined combination of SMTP commands. The goal of this script is to tell if a SMTP server is vulnerable to mail relaying. An SMTP server that works as an open relay, is a email server that does not verify if the user is authorised to send email from the specified email address. Therefore, users would be able to send email originating from any third-party email address that they want. The checks are done based in combinations of MAIL FROM and RCPT TO commands. The list is hardcoded in the source file. The script will output all the working combinations that the server allows if nmap is in verbose mode otherwise the script will print the number of successful tests. The script will not output if the server requires authentication. If debug is enabled and an error occurrs while testing the target host, the error will be printed with the list of any combinations that were found prior to the error. ]] --- -- @usage -- nmap --script smtp-open-relay.nse [--script-args smtp-open-relay.domain=,smtp-open-relay.ip=
,...] -p 25,465,587 -- -- @output -- Host script results: -- | smtp-open-relay: Server is an open relay (1/16 tests) -- |_MAIL FROM: -> RCPT TO: -- -- @args smtp.domain or smtp-open-relay.domain Define the domain to be used in the anti-spam tests and EHLO command (default -- is nmap.scanme.org) -- @args smtp-open-relay.ip Use this to change the IP address to be used (default is the target IP address) -- @args smtp-open-relay.from Define the source email address to be used (without the domain, default is -- antispam) -- @args smtp-open-relay.to Define the destination email address to be used (without the domain, default is -- relaytest) -- changelog -- 2007-05-16 Arturo 'Buanzo' Busleiman -- + Added some strings to return in different places -- * Changed "HELO www.[ourdomain]" to "EHLO [ourdomain]" -- * Fixed some API differences -- * The "ourdomain" variable's contents are used instead of hardcoded "insecure.org". Settable by the user. -- * Fixed tags -> categories (reported by Jason DePriest to nmap-dev) -- 2009-09-20 Duarte Silva -- * Rewrote the script -- + Added documentation and some more comments -- + Parameter to define the domain to be used instead of "ourdomain" variable -- + Parameter to define the IP address to be used instead of the target IP address -- * Script now detects servers that enforce authentication -- * Changed script categories from demo to discovery and intrusive -- * Renamed "spamtest" strings to "antispam" -- 2010-02-20 Duarte Silva -- * Renamed script parameters to follow the new naming convention -- * Fixed problem with broken connections -- * Changed script output to show all the successful tests -- * Changed from string concatenation to string formatting -- + External category -- + Now the script will issue the QUIT message as specified in the SMTP RFC -- 2010-02-27 Duarte Silva -- + More information in the script description -- + Script will output the reason for failed commands (at the connection level) -- * If some combinations were already found before an error, the script will report them -- 2010-03-07 Duarte Silva -- * Fixed socket left open when receive_lines function call fails -- * Minor comments changes -- 2010-03-14 Duarte Silva -- * Made the script a little more verbose -- 2011-06-03 -- * Rewrite the script to use the smtp.lua library. author = "Arturo 'Buanzo' Busleiman" license = "Same as Nmap--See http://nmap.org/book/man-legal.html" categories = {"discovery","intrusive","external"} require "shortport" require "stdnse" require "smtp" portrule = shortport.port_or_service({ 25, 465, 587 }, { "smtp", "smtps", "submission" }) ---Gets the user specified parameters to be used in the tests. -- --@param host Target host (used for the ip parameter default value) --@return Domain, from, to and ip to be used in the tests function get_parameters(host) -- call smtp.get_domain() without the host table to use the -- 'nmap.scanme.org' host name, we are scanning for open relays. local domain = stdnse.get_script_args('smtp-open-relay.domain') or smtp.get_domain() local from = stdnse.get_script_args('smtp-open-relay.from') or "antispam" local to = stdnse.get_script_args('smtp-open-relay.to') or "relaytest" local ip = stdnse.get_script_args('smtp-open-relay.ip') or host.ip return domain, from, to, ip end function go(host, port) local options = { timeout = 10000, recv_before = true, ssl = true, } local result, status, index = {} local domain, from, to, ip = get_parameters(host) local socket, response = smtp.connect(host, port, options) if not socket then return false, string.format("Couldn't establish connection on port %i", port.number) end local srvname = string.match(response, "%d+%s([%w]+[%w\.\-]*)") local status, response = smtp.ehlo(socket, domain) if not status then return status, response end if not srvname then srvname = string.match(response, "%d+%-([%w]+[%w\.\-]*)") end -- Antispam tests. local tests = { { from = "", to = string.format("%s@%s", to, domain) }, { from = string.format("%s@%s", from, domain), to = string.format("%s@%s", to, domain) }, { from = string.format("%s@%s", from, srvname), to = string.format("%s@%s", to, domain) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s@%s", to, domain) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s%%%s@[%s]", to, domain, ip) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s%%%s@%s", to, domain, srvname) }, { from = string.format("%s@[%s]", from, ip), to = string.format("\"%s@%s\"", to, domain) }, { from = string.format("%s@[%s]", from, ip), to = string.format("\"%s%%%s\"", to, domain) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s@%s@[%s]", to, domain, ip) }, { from = string.format("%s@[%s]", from, ip), to = string.format("\"%s@%s\"@[%s]", to, domain, ip) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s@%s@%s", to, domain, srvname) }, { from = string.format("%s@[%s]", from, ip), to = string.format("@[%s]:%s@%s", ip, to, domain) }, { from = string.format("%s@[%s]", from, ip), to = string.format("@%s:%s@%s", srvname, to, domain) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s!%s", domain, to) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s!%s@[%s]", domain, to, ip) }, { from = string.format("%s@[%s]", from, ip), to = string.format("%s!%s@%s", domain, to, srvname) }, } -- This function is used when something goes wrong with the connection. -- It makes sure that if it found working combinations before the error -- occurred, they will be returned. If the debug flag is enabled the -- error message will be appended to the combinations list. local failure = function(message) if #result > 0 then table.insert(result, message) return true, result else return false, message end end for index = 1, #tests do status, response = smtp.reset(socket) if not status then if string.match(response, "530") then return false, "Server isn't an open relay, authentication needed" end return failure(response) end status, response = smtp.query(socket, "MAIL", string.format("FROM:<%s>", tests[index]["from"])) -- If this command fails to be sent, then something went -- wrong with the connection. if not status then return failure(string.format("Failed to issue %s command (%s)", tests[index]["from"], response)) end if string.match(response, "530") then smtp.quit(socket) return false, "Server isn't an open relay, authentication needed" elseif smtp.check_reply("MAIL", response) then -- Lets try to actually relay. status, response = smtp.query(socket, "RCPT", string.format("TO:<%s>", tests[index]["to"])) if not status then return failure(string.format("Failed to issue %s command (%s)", tests[index]["to"], response)) end if string.match(response, "530") then smtp.quit(socket) return false, "Server isn't an open relay, authentication needed" elseif smtp.check_reply("RCPT", response) then -- Save the working from and to combination. table.insert(result, string.format("MAIL FROM:<%s> -> RCPT TO:<%s>", tests[index]["from"], tests[index]["to"])) end end end smtp.quit(socket) return true, result end action = function(host, port) local status, result = go(host, port) -- The go function returned false, this means that the result is -- a simple error message. if not status then return result else -- Combinations were found. If verbosity is active, the script -- will print all the successful tests. Otherwise it will only -- print the conclusion. if #result > 0 then final = {} table.insert(final, string.format("Server is an open relay (%i/16 tests)", (#result))) if nmap.verbosity() > 1 then for index, test in ipairs(result) do table.insert(final, test) end end return stdnse.strjoin("\n ", final) end return "Server doesn't seem to be an open relay, all tests failed" end end