tls-hellofirst - Audit TLS implementations for handshake reversal. https://twitter.com/bonsaiviking/status/580727089944518656

tls-hellofirst.nse

local nmap = require "nmap"
local shortport = require "shortport"
local stdnse = require "stdnse"
local table = require "table"
local bin = require "bin"
local tls = require "tls"

description = [[
Tries to confuse a TLS server into sending a ClientHello by first sending a HelloRequest.

No server implementations are known to be vulnerable
]]

---
-- @usage
-- nmap --script=tls-hellofirst
--
--@output
-- 443/tcp open  https
-- | tls-hellofirst: 
-- |   type: handshake
-- |   body: 
-- |     
-- |       type: client_hello
-- |       data: \x00\x00U\x12\xF8{j\xEA\x05fp\xD4\xDA\xA0\xE4s8\x83\xD5!.:\x89S\x7F\xA1\xAC\xCE\xEB\x87e\xBA\x94\x0C\x00\x00\x08\x00\x04\x00\x05\x00	\x00
-- | \x01\x00
-- |   length: 51
-- |_  protocol: TLSv1.0
--
-- @xmloutput
-- <elem key="type">handshake</elem>
-- <table key="body">
--   <table>
--     <elem key="type">client_hello</elem>
--     <elem key="data">\x00\x00U\x12\xF8{j\xEA\x05fp\xD4\xDA\xA0\xE4s8\x83\xD5!.:\x89S\x7F\xA1\xAC\xCE\xEB\x87e\xBA\x94\x0C\x00\x00\x08\x00\x04\x00\x05\x00&#x9;\x00&#xa;\x01\x00</elem>
--   </table>
-- </table>
-- <elem key="length">51</elem>
-- <elem key="protocol">TLSv1.0</elem>


author = "Daniel Miller"

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

categories = {"discovery"}

portrule = shortport.ssl


local wrong_hello = function(host, port)
  local hello_request = tls.record_write( "handshake", "SSLv3",
    bin.pack(">Cxxx", tls.TLS_HANDSHAKETYPE_REGISTRY["hello_request"]))

  -- Connect to the target server
  local sock = nmap.new_socket()
  local ct = stdnse.get_timeout(host)
  -- fast timeout for TCP connect
  sock:set_timeout(ct)
  local status, err = sock:connect(host, port)
  if not status then
    sock:close()
    stdnse.debug1("Can't send: %s", err)
    return false
  end
  -- slower timeout for TLS host processing
  sock:set_timeout(ct+4000)
  -- Some services send stuff right away: that's not what we're looking for
  -- Example: osiris Host IDS agent sends a client_hello immediately on connect.
  status, err = sock:receive_bytes(1)
  if status then
    sock:close()
    stdnse.debug1("Service isn't server TLS (Sent data first)")
    return false
  end

  -- Send HelloRequest to the target server
  status, err = sock:send(hello_request)
  if not status then
    stdnse.debug1("Couldn't send: %s", err)
    sock:close()
    return false
  end

  -- Read response
  local response
  status, response, err = tls.record_buffer(sock)
  if not status then
    stdnse.debug1("Couldn't receive: %s", err)
    sock:close()
    return false
  end

  return true, response
end

local check_response = function(response)
  local i, record = tls.record_read(response, 0)
  if record == nil then
    stdnse.debug1("Unknown response from server")
    return nil
  end

  if record.type == "alert" then
    stdnse.debug1("Server properly sent alert")
    return nil
  end

  return record

end

action = function(host, port)
  local status, response

  -- Send hello-request
  status, response = wrong_hello(host, port)
  if status and response then
    -- Analyze response
    local results = check_response(response)
    return results
  end
end