banner
NSE detection rule by jah · Same as Nmap--See https://nmap.org/book/man-legal.html
A simple banner grabber which connects to an open TCP port and prints out anything sent by the listening service within five seconds.
The banner will be truncated to fit into a single line, but an extra line may be printed for every
increase in the level of verbosity requested on the command line.
local comm = require "comm"
local nmap = require "nmap"
local stdnse = require "stdnse"
local shortport = require "shortport"
local table = require "table"
local U = require "lpeg-utility"
description = [[
A simple banner grabber which connects to an open TCP port and prints out anything sent by the listening service within five seconds.
The banner will be truncated to fit into a single line, but an extra line may be printed for every
increase in the level of verbosity requested on the command line.
]]
---
-- @output
-- 21/tcp open ftp
-- |_ banner: 220 FTP version 1.0\x0D\x0A
-- @arg banner.ports Which ports to grab. Same syntax as -p option. Use
-- "common" to only grab common text-protocol banners.
-- Default: all ports.
-- @arg banner.timeout How long to wait for a banner. Default: 5s
author = "jah"
license = "Same as Nmap--See https://nmap.org/book/man-legal.html"
categories = {"discovery", "safe"}
local portarg = stdnse.get_script_args(SCRIPT_NAME .. ".ports")
if portarg then
if portarg == "common" then
portarg = "13,17,21-23,25,129,194,587,990,992,994,6667,6697"
end
-- ensure TCP
portarg = portarg:gsub("^[T:]*", "T:")
portrule = shortport.port_range(portarg)
else
portrule = function(host, port) return port.protocol == "tcp" end
end
---
-- Grabs a banner and outputs it nicely formatted.
action = function( host, port )
local out = grab_banner(host, port)
return output( out )
end
---
-- Connects to the target on the given port and returns any data issued by a listening service.
-- @param host Host Table.
-- @param port Port Table.
-- @return String or nil if data was not received.
function grab_banner(host, port)
-- Did the service engine already do the hard work?
if port.version and port.version.service_fp then
local response = U.get_response(port.version.service_fp, "NULL")
if response then
return response:match("^%s*(.-)%s*$");
end
end
local opts = {}
opts.timeout = stdnse.parse_timespec(stdnse.get_script_args(SCRIPT_NAME .. ".timeout"))
opts.timeout = (opts.timeout or 5) * 1000
local status, response = comm.get_banner(host, port, opts)
if not status then
local errlvl = { ["EOF"]=3,["TIMEOUT"]=3,["ERROR"]=2 }
stdnse.debug(errlvl[response] or 1, "failed for %s on %s port %s. Message: %s", host.ip, port.protocol, port.number, response or "No Message.")
return nil
end
return response:match("^%s*(.-)%s*$");
end
---
-- Formats the banner for printing to the port script result.
--
-- Non-printable characters are hex encoded and the banner is
-- then truncated to fit into the number of lines of output desired.
-- @param out String banner issued by a listening service.
-- @return String formatted for output.
function output( out )
if type(out) ~= "string" or out == "" then return nil end
local filename = SCRIPT_NAME
local line_len = 75 -- The character width of command/shell prompt window.
local fline_offset = 5 -- number of chars excluding script id not available to the script on the first line
-- number of chars available on the first line of output
-- we'll skip the first line of output if the filename is looong
local fline_len
if filename:len() < (line_len-fline_offset) then
fline_len = line_len -1 -filename:len() -fline_offset
else
fline_len = 0
end
-- number of chars allowed on subsequent lines
local sline_len = line_len -1 -(fline_offset-2)
-- total number of chars allowed for output (based on verbosity)
local total_out_chars
if fline_len > 0 then
total_out_chars = fline_len + (extra_output()*sline_len)
else
-- skipped the first line so we'll have an extra lines worth of chars
total_out_chars = (1+extra_output())*sline_len
end
-- replace non-printable ascii chars - no need to do the whole string
out = replace_nonprint(out, 1+total_out_chars) -- 1 extra char so we can truncate below.
-- truncate banner to total_out_chars ensuring we remove whole hex encoded chars
if out:len() > total_out_chars then
while out:len() > total_out_chars do
if (out:sub(-4,-1)):match("\\x%x%x") then
out = out:sub(1,-1-4)
else
out = out:sub(1,-1-1)
end
end
out = ("%s..."):format(out:sub(1,total_out_chars-3)) -- -3 for ellipsis
end
-- break into lines - this will look awful if line_len is more than the actual space available on a line...
local ptr = fline_len
local t = {}
while true do
if out:len() >= ptr then
t[#t+1] = (ptr > 0 and out:sub(1,ptr)) or " " -- single space if we skipped the first line
out = out:sub(ptr+1,-1)
ptr = sline_len
else
t[#t+1] = out
break
end
end
return table.concat(t,"\n")
end
---
-- Replaces characters with ASCII values outside of the range of standard printable
-- characters (decimal 32 to 126 inclusive) with hex encoded equivalents.
--
-- The second parameter dictates the number of characters to return, however, if the
-- last character before the number is reached is one that needs replacing then up to
-- three characters more than this number may be returned.
-- If the second parameter is nil, no limit is applied to the number of characters
-- that may be returned.
-- @param s String on which to perform substitutions.
-- @param len Number of characters to return.
-- @return String.
function replace_nonprint( s, len )
local t = {}
local count = 0
for c in s:gmatch(".") do
if c:byte() < 32 or c:byte() > 126 then
t[#t+1] = ("\\x%s"):format( ("0%s"):format( ( (stdnse.tohex( c:byte() )):upper() ) ):sub(-2,-1) ) -- capiche
count = count+4
else
t[#t+1] = c
count = count+1
end
if type(len) == "number" and count >= len then break end
end
return table.concat(t)
end
---
-- Returns a number for each level of verbosity specified on the command line.
--
-- Ignores level increases resulting from debugging level.
-- @return Number
function extra_output()
return (nmap.verbosity()-nmap.debugging()>0 and nmap.verbosity()-nmap.debugging()) or 0
end