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telnet-brute.nse
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telnet-brute.nse
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local comm = require "comm"
local nmap = require "nmap"
local shortport = require "shortport"
local stdnse = require "stdnse"
local strbuf = require "strbuf"
local string = require "string"
local unpwdb = require "unpwdb"
description = [[
Tries to get Telnet login credentials by guessing usernames and passwords.
]]
author = "Eddie Bell, Ron Bowes"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {'brute', 'intrusive'}
---
-- @output
-- PORT STATE SERVICE
-- 23/tcp open telnet
-- |_telnet-brute: root - 1234
-- Update (Ron Bowes, November, 2009): Now uses unpwdb database.
local soc
local catch = function() soc:close() end
local try = nmap.new_try(catch)
portrule = shortport.port_or_service(23, 'telnet')
local escape_cred = function(cred)
if cred == '' then
return '<blank>'
else
return cred
end
end
---
-- Go through telnet's option palaver so we can get to the login prompt.
-- We just deny every options the server asks us about.
local negotiate_options = function(result, soc)
local index, x, opttype, opt, retbuf
index = 0
retbuf = strbuf.new()
while true do
-- 255 is IAC (Interpret As Command)
index, x = string.find(result, '\255', index)
if not index then
break
end
opttype = string.byte(result, index+1)
opt = string.byte(result, index+2)
-- don't want it! won't do it!
if opttype == 251 or opttype == 252 then
opttype = 254
elseif opttype == 253 or opttype == 254 then
opttype = 252
end
retbuf = retbuf .. string.char(255)
retbuf = retbuf .. string.char(opttype)
retbuf = retbuf .. string.char(opt)
index = index + 1
end
soc:send(strbuf.dump(retbuf))
end
---
-- A semi-state-machine that takes action based on output from the
-- server. Through pattern matching, it tries to deem if a user/pass
-- pair is valid. Telnet does not have a way of telling the client
-- if it was authenticated....so we have to make an educated guess
local brute_line = function(line, user, pass, usent, soc)
if (line:find 'incorrect' or line:find 'failed' or line:find 'denied' or
line:find 'invalid' or line:find 'bad') and usent then
usent = false
return 2, nil, usent
elseif (line:find '[/>%%%$#]+' or line:find "last login%s*:" or
line:find '%u:\\') and not
(line:find 'username%s*:' and line:find 'login%s*:') and
usent then
return 1, escape_cred(user) .. ' - ' .. escape_cred(pass) .. '\n', usent
elseif line:find 'username%s*:' or line:find 'login%s*:' then
try(soc:send(user .. '\r\0'))
usent = true
elseif line:find 'password%s*:' or line:find 'passcode%s*:' then
-- fix, add 'password only' support
if not usent then return 1, nil, usent end
try(soc:send(pass .. '\r\0'))
end
return 0, nil, usent
end
--[[
Splits the input into lines and passes it to brute_line()
so it can try to login with <user> and <pass>
return value:
(1, user:pass) - valid pair
(2, nil) - invalid pair
(3, nil) - disconnected and invalid pair
(4, nil) - disconnected and didn't send pair
--]]
local brute_cred = function(user, pass, soc)
local status, ret, value, usent, results
usent = false ; ret = 0
while true do
status, results = soc:receive_lines(1)
-- remote host disconnected
if not status then
if usent then return 3
else return 4
end
end
if (string.byte(results, 1) == 255) then
negotiate_options(results, soc)
end
results = string.lower(results)
for line in results:gmatch '[^\r\n]+' do
ret, value, usent = brute_line(line, user, pass, usent, soc)
if (ret > 0) then
return ret, value
end
end
end
return 1, "error -> this should never happen"
end
action = function(host, port)
local pair, status
local user, pass, count, rbuf
local usernames, passwords
status, usernames = unpwdb.usernames()
if(not(status)) then
stdnse.format_output(false, usernames)
end
status, passwords = unpwdb.passwords()
if(not(status)) then
return stdnse.format_output(false, passwords)
end
pair = nil
status = 3
count = 0
local opts = {timeout=4000}
local soc, line, best_opt = comm.tryssl(host, port, "\n",opts)
if not soc then
return stdnse.format_output(false, "Unable to open connection")
end
-- continually try user/pass pairs (reconnecting, if we have to)
-- until we find a valid one or we run out of pairs
pass = passwords()
while not (status == 1) do
if status == 2 or status == 3 then
user = usernames()
if(not(user)) then
usernames('reset')
user = usernames()
pass = passwords()
if(not(pass)) then
return stdnse.format_output(true, "No accounts found")
end
end
stdnse.print_debug(2, "telnet-brute: Trying %s/%s", user, pass)
end
-- make sure we don't get stuck in a loop
if status == 4 then
count = count + 1
if count > 3 then
return false, nil
end
else
count = 0
end
if status == 3 or status == 4 then
try(soc:connect(host, port, best_opt))
end
status, pair = brute_cred(user, pass, soc)
end
soc:close()
return pair
end