o [NSE] Added the script smtp-brute that performs brute force password

auditing against SMTP servers. [Patrik]

o [NSE] Updated SMTP library to support authentication using both plain-text
  and the SASL library. [Patrik]

scripts/script.db

@@ -184,6 +184,7 @@ Entry { filename = "smb-security-mode.nse", categories = { "discovery", "safe",
 Entry { filename = "smb-server-stats.nse", categories = { "discovery", "intrusive", } }
 Entry { filename = "smb-system-info.nse", categories = { "discovery", "intrusive", } }
 Entry { filename = "smbv2-enabled.nse", categories = { "default", "safe", } }
+Entry { filename = "smtp-brute.nse", categories = { "brute", "intrusive", } }
 Entry { filename = "smtp-commands.nse", categories = { "default", "discovery", "safe", } }
 Entry { filename = "smtp-enum-users.nse", categories = { "discovery", "external", "intrusive", } }
 Entry { filename = "smtp-open-relay.nse", categories = { "discovery", "external", "intrusive", } }

scripts/smtp-brute.nse

@@ -0,0 +1,136 @@
+description = [[
+Performs password guessing 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 - Account is valid
+-- |     lane:sniper - Account is valid
+-- |     parker:scorpio - Account is valid
+-- |   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>
+
+require 'creds'
+require 'brute'
+require 'shortport'
+require 'smtp'
+
+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	
+	status, result = engine:start()
+	
+	for _, sock in pairs(ConnectionPool) do sock:close() end
+	
+	return result
+end