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local bin = require "bin"
local nmap = require "nmap"
local shortport = require "shortport"
local stdnse = require "stdnse"
local table = require "table"
description = [[
Determines whether the encryption option is supported on a remote telnet
server. Some systems (including FreeBSD and the krb5 telnetd available in many
Linux distributions) implement this option incorrectly, leading to a remote
root vulnerability. This script currently only tests whether encryption is
supported, not for that particular vulnerability.
References:
* FreeBSD Advisory: http://lists.freebsd.org/pipermail/freebsd-announce/2011-December/001398.html
* FreeBSD Exploit: http://www.exploit-db.com/exploits/18280/
* RedHat Enterprise Linux Advisory: https://rhn.redhat.com/errata/RHSA-2011-1854.html
]]
---
-- @usage
-- nmap -p 23 <ip> --script telnet-encryption
--
-- @output
-- PORT STATE SERVICE REASON
-- 23/tcp open telnet syn-ack
-- | telnet-encryption:
-- |_ Telnet server supports encryption
--
--
categories = {"safe", "discovery"}
portrule = shortport.port_or_service(23, 'telnet')
author = {"Patrik Karlsson", "David Fifield", "Fyodor"}
license = "Same as Nmap--See https://nmap.org/book/man-legal.html"
local COMMAND = {
SubCommand = 0xFA,
Will = 0xFB,
Do = 0xFD,
Dont = 0xFE,
Wont = 0xFC,
}
local function processOptions(data)
local pos = 1
local result = {}
while ( pos < #data ) do
local iac, cmd, option
pos, iac, cmd = bin.unpack("CC", data, pos)
if ( 0xFF ~= iac ) then
break
end
if ( COMMAND.SubCommand == cmd ) then
repeat
pos, iac = bin.unpack("C", data, pos)
until( pos == #data or 0xFF == iac )
pos, cmd = bin.unpack("C", data, pos)
if ( not(cmd) == 0xF0 ) then
return false, "Failed to parse options"
end
else
pos, option = bin.unpack("H", data, pos)
result[option] = result[option] or {}
table.insert(result[option], cmd)
end
end
return true, { done=( not(#data == pos - 1) ), cmds = result }
end
local function fail(err) return stdnse.format_output(false, err) end
action = function(host, port)
local socket = nmap.new_socket()
local status = socket:connect(host, port)
local data = stdnse.fromhex( "FFFD26FFFB26")
local result
socket:set_timeout(7500)
status, result = socket:send(data)
if ( not(status) ) then
return fail(("Failed to send packet: %s"):format(result))
end
repeat
status, data = socket:receive()
if ( not(status) ) then
return fail(("Receiving packet: %s"):format(data))
end
status, result = processOptions(data)
if ( not(status) ) then
return fail("Failed to process telnet options")
end
until( result.done or result.cmds['26'] )
for _, cmd in ipairs(result.cmds['26'] or {}) do
if ( COMMAND.Will == cmd or COMMAND.Do == cmd ) then
return "\n Telnet server supports encryption"
end
end
return "\n Telnet server does not support encryption"
end
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