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✏️ Editing: ftp-syst.nse

local ftp = require "ftp"
local shortport = require "shortport"
local stdnse = require "stdnse"

description = [[
Sends FTP SYST and STAT commands and returns the result.

The canonical SYST response of "UNIX Type: L8" is stripped or ignored, since it
is meaningless. Typical FTP response codes (215 for SYST and 211 for STAT) are
also hidden.

References:
* https://cr.yp.to/ftp/syst.html
]]

author = "Daniel Miller"
license = "Same as Nmap--See https://nmap.org/book/man-legal.html"
categories = {"default", "discovery", "safe"}

portrule = shortport.port_or_service({21,990}, {"ftp","ftps"})

local function do_syst(socket, buffer)
end

action = function(host, port)
  local socket, code, message, buffer = ftp.connect(host, port)
  if not socket then
    stdnse.debug1("Couldn't connect: %s", code or message)
    return nil
  end
  if code and code ~= 220 then
    stdnse.debug1("banner code %d %q.", code, message)
    return nil
  end

-- SYST
  local auth_done = false
  local syst = nil
  repeat
    if not socket:send("SYST\r\n") then
      return nil
    end
    code, message = ftp.read_reply(buffer)
    if not code then
      stdnse.debug1("SYST error: %s", message)
      break
    end
    if code == 215 then
      local stripped = message:gsub("^UNIX Type: L8 *", "")
      if stripped ~= "" then
        syst = stripped
      end
      break
    elseif code < 300 then
      syst = ("%d %s"):format(code, message)
      break
    elseif not auth_done and -- we haven't tried logging in yet
      ( code == 503 -- Command SYST not accepted during Connected
        or code == 521 -- Not logged in - Secure authentication required
        or (code % 100) // 10 == 3 -- x3x codes are auth-related
        ) then
      -- Try logging in
      local status, code, message = ftp.auth(socket, buffer, "anonymous", "IEUser@")
      if status then
        auth_done = true
      end
    else
      stdnse.debug1("SYST error: %d %s", code, message)
      break
    end
  until not auth_done

-- STAT
  if not socket:send("STAT\r\n") then
    if syst then
      return {SYST=syst}
    else
      return nil
    end
  end

local out = stdnse.output_table()
  out.SYST = syst
  local code, stat = ftp.read_reply(buffer)

if code then
    if code == 211 then
      out.STAT = "\n" .. stat
    elseif code < 300 then
      out.STAT = ("%d\n%s"):format(code, stat)
    end
  end

ftp.close(socket)

if #out > 0 then
    return out
  end
end

MR SKB