local brute = require "brute"
local coroutine = require "coroutine"
local creds = require "creds"
local shortport = require "shortport"
local smtp = require "smtp"
local stdnse = require "stdnse"

description = [[
Performs brute force password auditing against SMTP servers using either LOGIN, PLAIN, CRAM-MD5, DIGEST-MD5 or NTLM authentication.
]]

---
-- @usage
-- nmap -p 25 --script smtp-brute <host>
--
-- @output
-- PORT    STATE SERVICE REASON
-- 25/tcp  open  stmp    syn-ack
-- | smtp-brute: 
-- |   Accounts
-- |     braddock:jules - Valid credentials
-- |     lane:sniper - Valid credentials
-- |     parker:scorpio - Valid credentials
-- |   Statistics
-- |_    Performed 1160 guesses in 41 seconds, average tps: 33
--
-- @args smtp-brute.auth authentication mechanism to use LOGIN, PLAIN, 
--		 CRAM-MD5, DIGEST-MD5 or NTLM

-- Version 0.1
-- Created 07/15/2011 - v0.1 - created by Patrik Karlsson <patrik@cqure.net>


author = "Patrik Karlsson"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"brute", "intrusive"}

portrule = shortport.port_or_service({ 25, 465, 587 },
                { "smtp", "smtps", "submission" })

local mech

-- By using this connectionpool we don't need to reconnect the socket
-- for each attempt.
ConnectionPool = {}

Driver = 
{

	-- Creates a new driver instance
	-- @param host table as received by the action method
	-- @param port table as received by the action method
	-- @param pool an instance of the ConnectionPool
	new = function(self, host, port)
		local o = { host = host, port = port }
       	setmetatable(o, self)
        self.__index = self
		return o
	end,
	
	-- Connects to the server (retrieves a connection from the pool)
	connect = function( self )
		self.socket = ConnectionPool[coroutine.running()]
		if ( not(self.socket) ) then
			self.socket = smtp.connect(self.host, self.port, { ssl = true, recv_before = true })
			if ( not(self.socket) ) then return false end
			ConnectionPool[coroutine.running()] = self.socket
		end
		return true
	end,

	-- Attempts to login to the server
	-- @param username string containing the username
	-- @param password string containing the password
	-- @return status true on success, false on failure
	-- @return brute.Error on failure and brute.Account on success
	login = function( self, username, password )
		local status, err = smtp.login( self.socket, username, password, mech )
		if ( status ) then
			smtp.quit(self.socket)
			ConnectionPool[coroutine.running()] = nil
			return true, brute.Account:new(username, password, creds.State.VALID)
		end
		if ( err:match("^ERROR: Failed to .*") ) then
			self.socket:close()
			ConnectionPool[coroutine.running()] = nil
			local err = brute.Error:new( err )
			-- This might be temporary, set the retry flag
			err:setRetry( true )
			return false, err			
		end
		return false, brute.Error:new( "Incorrect password" )
	end,
	
	-- Disconnects from the server (release the connection object back to
	-- the pool)
	disconnect = function( self )
		return true
	end,
		
}


action = function(host, port)

	local socket, response = smtp.connect(host, port, { ssl = true, recv_before = true })
	if ( not(socket) ) then return "\n  ERROR: Failed to connect to SMTP server" end
	local status, response = smtp.ehlo(socket, smtp.get_domain(host))
	if ( not(status) ) then return "\n  ERROR: EHLO command failed, aborting ..." end
	local mechs = smtp.get_auth_mech(response)
	if ( not(mechs) ) then 
		return "\n  ERROR: Failed to retrieve authentication mechanisms form server"
	end
	smtp.quit(socket)
		
	local mech_prio = stdnse.get_script_args("smtp-brute.auth") 
	mech_prio = ( mech_prio and { mech_prio } ) or 
					{ "LOGIN", "PLAIN", "CRAM-MD5", "DIGEST-MD5", "NTLM" }
	
	for _, mp in ipairs(mech_prio) do
		for _, m in pairs(mechs) do 
			if ( mp == m ) then
				mech = m
				break
			end
		end
		if ( mech ) then break end
	end
		
	local engine = brute.Engine:new(Driver, host, port)
	
	engine.options.script_name = SCRIPT_NAME
	local result
	status, result = engine:start()
	
	for _, sock in pairs(ConnectionPool) do sock:close() end
	
	return result
end
