local io = require "io"
local nmap = require "nmap"
local string = require "string"
local shortport = require "shortport"
local sip = require "sip"
local stdnse = require "stdnse"
local table = require "table"
local math = require "math"
local brute = require "brute"
local creds = require "creds"
local unpwdb = require "unpwdb"

description = [[
Enumerates a SIP server's valid extensions (users).

The script works by sending REGISTER SIP requests to the server with the
specified extension and checking for the response status code in order
to know if an extension is valid. If a response status code is 401 or
407, it means that the extension is valid and requires authentication. If the
response status code is 200, it means that the extension exists and doesn't
require any authentication while a 403 response status code means that
extension exists but access is forbidden. To skip false positives, the script
begins by sending a REGISTER request for a random extension and checking for
response status code.
]]

---
--@args sip-enum-users.minext Extension value to start enumeration from.
--  Defaults to <code>0</code>.
-- 
--@args sip-enum-users.maxext Extension value to end enumeration at.
--  Defaults to <code>999</code>.
--
--@args sip-enum-users.padding Number of digits to pad zeroes up to. 
--  Defaults to <code>0</code>. No padding if this is set to zero.
--
--@args sip-enum-users.users If set, will also enumerate users 
--  from <code>userslist</code> file.
--
--@args sip-enum-users.userslist Path to list of users.
--  Defaults to <code>nselib/data/usernames.lst</code>.
--
--@usage
-- nmap --script=sip-enum-users -sU -p 5060 <targets>
--
-- nmap --script=sip-enum-users -sU -p 5060 <targets> --script-args 
-- 'sip-enum-users.padding=4, sip-enum-users.minext=1000,
-- sip-enum-users.maxext=9999'
--
--@output
-- 5060/udp open sip
-- | sip-enum-users: 
-- |   Accounts
-- |     101: Auth required
-- |     120: No auth
-- |   Statistics
-- |_    Performed 1000 guesses in 50 seconds, average tps: 20


author = "Hani Benhabiles"

license = "Same as Nmap--See http://nmap.org/book/man-legal.html"

categories = {"auth", "intrusive"}


portrule = shortport.port_or_service(5060, "sip", {"tcp", "udp"})

--- Function that sends register sip request with provided extension 
-- using the specified session.
-- @arg sess session to use.
-- @arg ext Extension to send register request to.
-- @return status true on success, false on failure.
-- @return Response instance on success, error string on failure.
local registerext = function(sess, ext)
    -- set session values
    local request = sip.Request:new(sip.Method.REGISTER)

    request:setUri("sip:" ..  sess.sessdata:getServer())
    sess.sessdata:setUsername(ext)
    request:setSessionData(sess.sessdata)
    
    return sess:exch(request)
end

--- Function that returns a number as string with a number of zeroes padded to
-- the left.
-- @arg num Number to be padded.
-- @arg padding number of digits to pad up to.
-- @return string of padded number.
local padnum = function(num, padding)
    -- How many zeroes do we need to add
    local n = #tostring(num)
    if n >= padding then
	return tostring(num)
    end
    n = padding - n

    return string.rep(tostring(0), n) .. tostring(num)
end

--- Iterator function that returns values from a lower value up to a greater
-- value with zeroes padded up to padding argument.
-- @arg minval Start value.
-- @arg maxval End value.
-- @arg padding number of digits to pad up to.
-- @return string current value.
local numiterator = function(minval, maxval, padding)
    local i = minval - 1
    return function()
	i = i + 1
	if i <= maxval then return padnum(i, padding), '' end
    end
end

--- Iterator function that returns lines from a file
-- @arg userslist Path to file list in data location.
-- @return status false if error.
-- @return string current line.
local useriterator = function(list)
    local f = nmap.fetchfile(list) or list
    if not f then
	return false, ("\n ERROR: Couldn't find %s"):format(list)
    end
    f = io.open(f)
    if ( not(f) ) then
	return false, ("\n  ERROR: Failed to open %s"):format(list)
    end
    return function()
	for line in f:lines() do
	    return line
	end
    end
end

--- function that tests for 404 status code when sending a REGISTER request
-- with a random sip extension.
-- @arg host Target host table.
-- @arg port Target port table.
local test404 = function(host, port)
    local session, status, randext, response
    -- Random extension
    randext = math.random(1234567,987654321)

    session = sip.Session:new(host, port)
    status = session:connect()
    if not status then
	return false, "ERROR: Failed to connect to the SIP server."
    end
    
    status, response = registerext(session, randext)
    if  not status then
	return false, "ERROR: No response from the SIP server."
    end
    if response:getErrorCode() ~= 404 then
	return false, "Server not returning 404 for random extension."
    end
    return true

end

Driver = {

    new = function(self, host, port)
	local o = {}
	setmetatable(o, self)
	self.__index = self
	o.host = host
	o.port = port
	return o
    end,

    connect = function( self )
	self.session = sip.Session:new(self.host, self.port)
	local status = self.session:connect()
	if ( not(status) ) then
	    return false, brute.Error:new( "Couldn't connect to host" )
	end
	return true
    end,

    login = function( self, username, password)
	-- We are using the "password" values instead of the "username" so we
	-- could benifit from brute.lua passonly option and setPasswordIterator
	-- function, as we are doing usernames enumeration only and not
	-- credentials brute forcing.
	local status, response, responsecode
	-- Send REGISTER request for each extension
	status, response = registerext(self.session, password)
	if status then
	    responsecode = response:getErrorCode()
	    -- If response status code is 401 or 407, then extension exists but
	    -- requires authentication
	    if responsecode == sip.Error.UNAUTHORIZED or
		responsecode == sip.Error.PROXY_AUTH_REQUIRED then
		return true, brute.Account:new(password, " Auth required", '')

		-- If response status code is 200, then extension exists
		-- and requires no authentication
	    elseif responsecode == sip.Error.OK then
		return true, brute.Account:new(password, " No auth", '')
		-- If response status code is 200, then extension exists
		-- but access is forbidden.

	    elseif responsecode == sip.Error.FORBIDDEN then
		return true, brute.Account:new(password, " Forbidden", '')
	    end
	    return false,brute.Error:new( "Not found" )
	else
	    return false,brute.Error:new( "No response" )
	end
    end,

    disconnect = function(self) 
	self.session:close()
	return true
    end,	
}

action = function(host, port)
    local result, lthreads = {}, {}
    local status, err 
    local minext = tonumber(stdnse.get_script_args(SCRIPT_NAME .. ".minext")) or 0
    local minext = tonumber(stdnse.get_script_args(SCRIPT_NAME .. ".minext")) or 0
    local maxext = tonumber(stdnse.get_script_args(SCRIPT_NAME .. ".maxext")) or 999
    local padding = tonumber(stdnse.get_script_args(SCRIPT_NAME .. ".padding")) or 0
    local users = stdnse.get_script_args(SCRIPT_NAME .. ".users")
    local usersfile = stdnse.get_script_args(SCRIPT_NAME .. ".userslist") 
			 or "nselib/data/usernames.lst"

    -- min extension should be less than max extension.
    if minext > maxext then
	return "ERROR: maxext should be greater or equal than minext."
    end
    -- If not set to zero, number of digits to pad up to should have less or
    -- equal the number of digits of max extension.
    if padding ~= 0 and #tostring(maxext) > padding then
	return "ERROR: padding should be greater or equal to number of digits of maxext."
    end

    -- We test for false positives by sending a request for a random extension
    -- and checking if it did return a 404.
    status, err = test404(host, port)
    if not status then
	return err
    end

    local engine = brute.Engine:new(Driver, host, port)
    engine.options.script_name = SCRIPT_NAME

    local iterator = numiterator(minext, maxext, padding)
    if users then
	local usernames, err = useriterator(usersfile)
	if not usernames then
	    return err
	end
	-- Concat numbers and users iterators
	iterator = unpwdb.concat_iterators(iterator, usernames)
    end
    engine:setPasswordIterator(iterator)
    engine.options.passonly = true
    status, result = engine:start()

    return result 
end