local bin = require "bin"
local bit = require "bit"
local ipOps = require "ipOps"
local math = require "math"
local nmap = require "nmap"
local os = require "os"
local smb = require "smb"
local stdnse = require "stdnse"
local string = require "string"
local table = require "table"

description = [[
Checks if a host is infected with Conficker.C or higher, based on Conficker's peer to peer communication. 

When Conficker.C or higher infects a system, it opens four ports: two TCP and two UDP. The ports are 
random, but are seeded with the current week and the IP of the infected host. By determining the algorithm, 
one can check if these four ports are open, and can probe them for more data. 

Once the open ports are found, communication can be initiated using Conficker's custom peer to peer protocol. 
If a valid response is received, then a valid Conficker infection has been found. 

This check won't work properly on a multihomed or NATed system because the open ports will be based on a nonpublic IP. 
The argument <code>checkall</code> tells Nmap to attempt communication with every open port (much like a version
check) and the argument <code>realip</code> tells Nmap to base its port generation on the given IP address instead
of the actual IP.

By default, this will run against a system that has a standard Windows port open (445, 139, 137). The arguments
<code>checkall</code> and <code>checkconficker</code> will both perform checks regardless of which port is open, see the args section for
more information. 

Note: Ensure your clock is correct (within a week) before using this script!

The majority of research for this script was done by Symantec Security Response, and some was taken 
from public sources (most notably the port blacklisting was found by David Fifield). A big thanks goes
out to everybody who contributed! 
]]

---
-- @args checkall If set to <code>1</code> or <code>true</code>, attempt
-- to communicate with every open port.
-- @args checkconficker If set to <code>1</code> or <code>true</code>, the script will always run on active hosts, 
--       it doesn't matter if any open ports were detected. 
-- @args realip An IP address to use in place of the one known by Nmap.
--
-- @usage
-- # Run the scripts against host(s) that appear to be Windows
-- nmap --script p2p-conficker,smb-os-discovery,smb-check-vulns --script-args=safe=1 -T4 -vv -p445 <host>
-- sudo nmap -sU -sS --script p2p-conficker,smb-os-discovery,smb-check-vulns --script-args=safe=1 -vv -T4 -p U:137,T:139 <host>
--
-- # Run the scripts against all active hosts (recommended)
-- nmap -p139,445 -vv --script p2p-conficker,smb-os-discovery,smb-check-vulns --script-args=checkconficker=1,safe=1 -T4 <host>
--
-- # Run scripts against all 65535 ports (slow)
-- nmap --script p2p-conficker,smb-os-discovery,smb-check-vulns -p- --script-args=checkall=1,safe=1 -vv -T4 <host>
--
-- # Base checks on a different ip address (NATed)
-- nmap --script p2p-conficker,smb-os-discovery -p445 --script-args=realip=\"192.168.1.65\" -vv -T4 <host>
--
-- @output
-- Clean machine (results printed only if extra verbosity ("-vv")is specified):
-- Host script results:
-- |  p2p-conficker: Checking for Conficker.C or higher...
-- |  | Check 1 (port 44329/tcp): CLEAN (Couldn't connect)
-- |  | Check 2 (port 33824/tcp): CLEAN (Couldn't connect)
-- |  | Check 3 (port 31380/udp): CLEAN (Failed to receive data)
-- |  | Check 4 (port 52600/udp): CLEAN (Failed to receive data)
-- |_ |_ 0/4 checks: Host is CLEAN or ports are blocked
-- 
-- Infected machine (results always printed):
-- Host script results:
-- |  p2p-conficker: Checking for Conficker.C or higher...
-- |  | Check 1 (port 18707/tcp): INFECTED (Received valid data)
-- |  | Check 2 (port 65273/tcp): INFECTED (Received valid data)
-- |  | Check 3 (port 11722/udp): INFECTED (Received valid data)
-- |  | Check 4 (port 12690/udp): INFECTED (Received valid data)
-- |_ |_ 4/4 checks: Host is likely INFECTED
-- 
-----------------------------------------------------------------------

author = "Ron Bowes (with research from Symantec Security Response)"
copyright = "Ron Bowes"
license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
categories = {"default","safe"}


-- Max packet size
local MAX_PACKET = 0x2000

-- Flags
local mode_flags =
{
	FLAG_MODE              = bit.lshift(1, 0),
	FLAG_LOCAL_ACK         = bit.lshift(1, 1),
	FLAG_IS_TCP            = bit.lshift(1, 2),
	FLAG_IP_INCLUDED       = bit.lshift(1, 3),
	FLAG_UNKNOWN0_INCLUDED = bit.lshift(1, 4),
	FLAG_UNKNOWN1_INCLUDED = bit.lshift(1, 5),
	FLAG_DATA_INCLUDED     = bit.lshift(1, 6),
	FLAG_SYSINFO_INCLUDED  = bit.lshift(1, 7),
	FLAG_ENCODED           = bit.lshift(1, 15)
}

---For a hostrule, simply use the 'smb' ports as an indicator, unless the user overrides it
hostrule = function(host)
	if ( nmap.address_family() ~= 'inet' ) then
		return false
	end
	if(smb.get_port(host) ~= nil) then
		return true
	elseif(nmap.registry.args.checkall == "true" or nmap.registry.args.checkall == "1") then
		return true
	elseif(nmap.registry.args.checkconficker == "true" or nmap.registry.args.checkconficker == "1") then
		return true
	end

	return false
end

-- Multiply two 32-bit integers and return a 64-bit product. The first return
-- value is the low-order 32 bits of the product and the second return value is
-- the high-order 32 bits.
--
--@param u First number (0 <= u <= 0xFFFFFFFF)
--@param v Second number (0 <= v <= 0xFFFFFFFF)
--@return 64-bit product of u*v, as a pair of 32-bit integers. 
local function mul64(u, v)
	-- This is based on formula (2) from section 4.3.3 of The Art of
	-- Computer Programming. We split u and v into upper and lower 16-bit
	-- chunks, such that
	--   u = 2**16 u1 + u0    and    v = 2**16 v1 + v0
	-- Then
	--   u v = (2**16 u1 + u0) * (2**16 v1 + v0)
	--       = 2**32 u1 v1 + 2**16 (u0 v1 + u1 v0) + u0 v0
	assert(0 <= u and u <= 0xFFFFFFFF)
	assert(0 <= v and v <= 0xFFFFFFFF)
	local u0, u1 = bit.band(u, 0xFFFF), bit.rshift(u, 16)
	local v0, v1 = bit.band(v, 0xFFFF), bit.rshift(v, 16)
	-- t uses at most 49 bits, which is within the range of exact integer
	-- precision of a Lua number.
	local t = u0 * v0 + (u0 * v1 + u1 * v0) * 65536
	return bit.band(t, 0xFFFFFFFF), u1 * v1 + bit.rshift(t, 32)
end

---Rotates the 64-bit integer defined by h:l left by one bit. 
--
--@param h The high-order 32 bits
--@param l The low-order 32 bits
--@return 64-bit rotated integer, as a pair of 32-bit integers. 
local function rot64(h, l)
	local i

	assert(0 <= h and h <= 0xFFFFFFFF)
	assert(0 <= l and l <= 0xFFFFFFFF)

	local tmp = bit.band(h, 0x80000000)     -- tmp  = h & 0x80000000
	h = bit.lshift(h, 1)                    -- h = h << 1
	h = bit.bor(h, bit.rshift(l, 31))       -- h = h | (l >> 31)
	l = bit.lshift(l, 1)
	if(tmp ~= 0) then
		l = bit.bor(l, 1)
	end

	h = bit.band(h, 0xFFFFFFFF)
	l = bit.band(l, 0xFFFFFFFF)

	return h, l
end


---Check if a port is Blacklisted. Thanks to David Fifield for determining the purpose of the "magic"
-- array:
-- <http://www.bamsoftware.com/wiki/Nmap/PortSetGraphics#conficker>
--
-- Basically, each bit in the blacklist array represents a group of 32 ports. If that bit is on, those ports
-- are blacklisted and will never come up. 
--
--@param port The port to check
--@return true if the port is blacklisted, false otherwise
local function is_blacklisted_port(port)
	local r, l

	local blacklist = { 0xFFFFFFFF, 0xFFFFFFFF, 0xF0F6BFBB, 0xBB5A5FF3, 0xF3977011, 0xEB67BFBF, 0x5F9BFAC8, 0x34D88091, 0x1E2282DF, 0x573402C4, 0xC0000084, 0x03000209, 0x01600002, 0x00005000, 0x801000C0, 0x00500040, 0x000000A1, 0x01000000, 0x01000000, 0x00022A20, 0x00000080, 0x04000000, 0x40020000, 0x88000000, 0x00000180, 0x00081000, 0x08801900, 0x00800B81, 0x00000280, 0x080002C0, 0x00A80000, 0x00008000, 0x00100040, 0x00100000, 0x00000000, 0x00000000, 0x10000008, 0x00000000, 0x00000000, 0x00000004, 0x00000002, 0x00000000, 0x00040000, 0x00000000, 0x00000000, 0x00000000, 0x00410000, 0x82000000, 0x00000000, 0x00000000, 0x00000001, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000008, 0x80000000, };

	r = bit.rshift(port, 5)
	l = bit.lshift(1, bit.band(r, 0x1f))
	r = bit.rshift(r, 5)

	return (bit.band(blacklist[r + 1], l) ~= 0)
end

---Generates the four random ports that Conficker uses, based on the current time and the IP address. 
--
--@param ip The IP address as a 32-bit little endian integer
--@param seed The seed, based on the time (<code>floor((time - 345600) / 604800)</code>)
--@return An array of four ports; the first and third are TCP, and the second and fourth are UDP. 
local function prng_generate_ports(ip, seed)
	local ports = {0, 0, 0, 0}
	local v1, v2
	local port1, port2, shift1, shift2
	local i
	local magic = 0x015A4E35

	stdnse.print_debug(1, "Conficker: Generating ports based on ip (0x%08x) and seed (%d)", ip, seed)

	v1 = -(ip + 1)
	repeat
		-- Loop 10 times to generate the first pair of ports
		for i = 0, 9, 1 do
			v1, v2 = mul64(bit.band(v1, 0xFFFFFFFF), bit.band(magic, 0xFFFFFFFF))

			-- Add 1 to v1, handling overflows
			if(v1 ~= 0xFFFFFFFF) then
				v1 = v1 + 1
			else
				v1 = 0
				v2 = v2 + 1
			end

			v2 = bit.rshift(v2, i)

			ports[(i % 2) + 1] = bit.bxor(bit.band(v2, 0xFFFF), ports[(i % 2) + 1])
		end
	until(is_blacklisted_port(ports[1]) == false and is_blacklisted_port(ports[2]) == false and ports[1] ~= ports[2])

	-- Update the accumlator with the seed
	v1 = bit.bxor(v1, seed)

	-- Loop 10 more times to generate the second pair of ports
	repeat
		for i = 0, 9, 1 do
			v1, v2 = mul64(bit.band(v1, 0xFFFFFFFF), bit.band(magic, 0xFFFFFFFF))

			-- Add 1 to v1, handling overflows
			if(v1 ~= 0xFFFFFFFF) then
				v1 = v1 + 1
			else
				v1 = 0
				v2 = v2 + 1
			end

			v2 = bit.rshift(v2, i)

			ports[(i % 2) + 3] = bit.bxor(bit.band(v2, 0xFFFF), ports[(i % 2) + 3])
		end
	until(is_blacklisted_port(ports[3]) == false and is_blacklisted_port(ports[4]) == false and ports[3] ~= ports[4])

	return {ports[1], ports[2], ports[3], ports[4]}
end

---Calculate a checksum for the data. This checksum is appended to every Conficker packet before the random noise. 
-- The checksum includes the key and data, but not the noise and optional length. 
--
--@param data The data to create a checksum for.
--@return An integer representing the checksum. 
local function p2p_checksum(data)
	local pos, i
	local hash = #data

	stdnse.print_debug(2, "Conficker: Calculating checksum for %d-byte buffer", #data)

	-- Get the first character
	pos, i = bin.unpack("<C", data)
	while i ~= nil do
		local h = bit.bxor(hash, i)
		-- Incorporate the current character into the checksum
		hash = bit.bor((h + h), bit.rshift(h, 31))
		hash = bit.band(hash, 0xFFFFFFFF)

		-- Get the next character
		pos, i = bin.unpack("<C", data, pos)
	end

	return hash
end

---Encrypt/decrypt the buffer with a simple xor-based symmetric encryption. It uses a 64-bit key, represented
-- by key1:key2, that is transmited in plain text. Since sniffed packets can be decrypted, this is a 
-- simple obfuscation technique. 
--
--@param packet The packet to encrypt (before the key and optional length are prepended). 
--@param key1 The low-order 32 bits in the key.
--@param key2 The high-order 32 bits in the key. 
--@return The encrypted (or decrypted) data. 
local function p2p_cipher(packet, key1, key2)
	local i
	local buf = ""

	for i = 1, #packet, 1 do
		-- Do a 64-bit rotate on key1:key2
		key2, key1 = rot64(key2, key1)

		-- Generate the key (the right-most byte)
		local k = bit.band(key1, 0x0FF)

		-- Xor the current character and add it to the encrypted buffer
		buf = buf .. string.char(bit.bxor(string.byte(packet, i), k))

		-- Update the key with 'k'
		key1 = key1 + k
		if(key1 > 0xFFFFFFFF) then
			-- Handle overflows
			key2 = key2 + (bit.rshift(key1, 32))
			key2 = bit.band(key2, 0xFFFFFFFF)
			key1 = bit.band(key1, 0xFFFFFFFF)
		end
	end

	return buf
end

---Decrypt the packet, verify it, and parse it. This function will fail with an error if the packet can't be
-- parsed properly (likely means the port is being used for something else), but will return successfully 
-- without checking the packet's checksum (although it does calculate the checksum). It's up to the calling
-- function to decide if it cares about the checksum. 
--
--@param packet The packet, without the optional length (if it's TCP). 
--@return (status, result) If status is true, result is a table (including 'hash' and 'real_hash'). If status
--        is false, result is a string that indicates why the parse failed. 
function p2p_parse(packet)
	local pos = 1
	local data = {}

	-- Get the key
	pos, data['key1'], data['key2'] = bin.unpack("<II", packet, pos)
	if(data['key2'] == nil) then
		return false, "Packet was too short [1]"
	end

	-- Decrypt the second half of the packet using the key
	packet = string.sub(packet, 1, pos - 1) .. p2p_cipher(string.sub(packet, pos), data['key1'], data['key2'])

	-- Parse the flags
	pos, data['flags'] = bin.unpack("<S", packet, pos)
	if(data['flags'] == nil) then
		return false, "Packet was too short [2]"
	end

	-- Get the IP, if it's present
	if(bit.band(data['flags'], mode_flags.FLAG_IP_INCLUDED) ~= 0) then
		pos, data['ip'], data['port'] = bin.unpack("<IS", packet, pos)
		if(data['ip'] == nil) then
			return false, "Packet was too short [3]"
		end
	end

	-- Read the first unknown value, if present
	if(bit.band(data['flags'], mode_flags.FLAG_UNKNOWN0_INCLUDED) ~= 0) then
		pos, data['unknown0'] = bin.unpack("<I", packet, pos)
		if(data['unknown0'] == nil) then
			return false, "Packet was too short [3]"
		end
	end

	-- Read the second unknown value, if present
	if(bit.band(data['flags'], mode_flags.FLAG_UNKNOWN1_INCLUDED) ~= 0) then
		pos, data['unknown1'] = bin.unpack("<I", packet, pos)
		if(data['unknown1'] == nil) then
			return false, "Packet was too short [4]"
		end
	end

	-- Read the data, if present
	if(bit.band(data['flags'], mode_flags.FLAG_DATA_INCLUDED) ~= 0) then
		pos, data['data_flags'], data['data_length'] = bin.unpack("<CS", packet, pos)
		if(data['data_length'] == nil) then
			return false, "Packet was too short [5]"
		end
		pos, data['data'] = bin.unpack(string.format("A%d", data['data_length']), packet, pos)
		if(data['data'] == nil) then
			return false, "Packet was too short [6]"
		end
	end

	-- Read the sysinfo, if present
	if(bit.band(data['flags'], mode_flags.FLAG_SYSINFO_INCLUDED) ~= 0) then
		pos, data['sysinfo_systemtestflags'], 
			data['sysinfo_os_major'], 
			data['sysinfo_os_minor'], 
			data['sysinfo_os_build'], 
			data['sysinfo_os_servicepack_major'], 
			data['sysinfo_os_servicepack_minor'], 
			data['sysinfo_ntdll_translation_file_information'], 
			data['sysinfo_prng_sample'], 
			data['sysinfo_unknown0'], 
			data['sysinfo_unknown1'], 
			data['sysinfo_unknown2'], 
			data['sysinfo_unknown3'], 
			data['sysinfo_unknown4'] = bin.unpack("<SCCSCCSISSISS", packet, pos)
		if(data['sysinfo_unknown4'] == nil) then
			return false, "Packet was too short [7]"
		end
	end

	-- Pull out the data that's used in the hash
	data['hash_data'] = string.sub(packet, 1, pos - 1)

	-- Read the hash
	pos, data['hash'] = bin.unpack("<I", packet, pos)
	if(data['hash'] == nil) then
		return false, "Packet was too short [8]"
	end

	-- Record the noise
	data['noise'] = string.sub(packet, pos)

	-- Generate the actual hash (we're going to ignore it for now, but it can be checked higher up)
	data['real_hash'] = p2p_checksum(data['hash_data'])

	return true, data
end

---Create a peer to peer packet for the given protocol. 
--
--@param protocol The protocol (either 'tcp' or 'udp' -- tcp packets have a length in front, and an extra
--       flag)
--@param do_encryption (optional) If set to false, packets aren't encrypted (the key '0' is used). Useful
--       for testing. Default: true.
local function p2p_create_packet(protocol, do_encryption)
	assert(protocol == "tcp" or protocol == "udp")

	local key1 = math.random(1, 0x7FFFFFFF)
	local key2 = math.random(1, 0x7FFFFFFF)

	-- A key of 0 disables the encryption
	if(do_encryption == false) then
		key1 = 0
		key2 = 0
	end

	local flags = 0

	-- Set a couple flags that we need (we don't send any optional data)
	flags = bit.bor(flags, mode_flags.FLAG_MODE)
	flags = bit.bor(flags, mode_flags.FLAG_ENCODED)
--	flags = bit.bor(flags, mode_flags.FLAG_LOCAL_ACK)
	-- Set the special TCP flag
	if(protocol == "tcp") then
		flags = bit.bor(flags, mode_flags.FLAG_IS_TCP)
	end

	-- Add the key and flags that are always present (and skip over the boring stuff)
	local packet = ""
	packet = packet .. bin.pack("<II", key1, key2)
	packet = packet .. bin.pack("<S", flags)

	-- Generate the checksum for the packet
	local hash = p2p_checksum(packet)
	packet = packet .. bin.pack("<I", hash)

	-- Encrypt the full packet, except for the key and optional length
	packet = string.sub(packet, 1, 8) .. p2p_cipher(string.sub(packet, 9), key1, key2)

	-- Add the length in front if it's TCP
	if(protocol == "tcp") then
		packet = bin.pack("<SA", #packet, packet)
	end

	return true, packet
end

---Checks if conficker is present on the given port/protocol. The ports Conficker uses are fairly standard, so
-- those should generally be used for this check. This can also be sent to any open port on the system. 
--
--@param ip The ip address of the system to check
--@param port The port to check (can be taken from <code>prng_generate_ports</code>, or from unidentified ports)
--@return (status, reason, data) Status indicates whether or not Conficker is suspected to be present (<code>true</code) = 
--        Conficker, <code>false</code> = no Conficker). If status is true, data is the table of information returned by 
--        Conficker. 
local function conficker_check(ip, port, protocol)
	local status, packet
	local socket
	local response

	status, packet = p2p_create_packet(protocol)
	if(status == false) then
		return false, packet
	end

	-- Try to connect to the first socket
	socket = nmap.new_socket()
	socket:set_timeout(5000)
	status, response = socket:connect(ip, port, protocol)
	if(status == false) then
		return false, "Couldn't establish connection (" .. response .. ")"
	end

	-- Send the packet
	socket:send(packet)

	-- Read a response (2 bytes minimum, because that's the TCP length)
	status, response = socket:receive_bytes(2)
	if(status == false) then
		return false, "Couldn't receive bytes: " .. response
	elseif(response == "ERROR") then
		return false, "Failed to receive data"
	elseif(response == "TIMEOUT") then
		return false, "Timeout"
	elseif(response == "EOF") then
		return false, "Couldn't connect"
	end

	-- If it's TCP, get the length and make sure we have the full packet
	if(protocol == "tcp") then
		local _, length = bin.unpack("<S", response, 1)

		while length > (#response - 2) do
			local response2

			status, response2 = socket:receive_bytes(2)
			if(status == false) then
				return false, "Couldn't receive bytes: " .. response2
			elseif(response2 == "ERROR") then
				return false, "Failed to receive data"
			elseif(response2 == "TIMEOUT") then
				return false, "Timeout"
			elseif(response2 == "EOF") then
				return false, "Couldn't connect"
			end

			response = response .. response2
		end

		-- Remove the 'length' bytes
		response = string.sub(response, 3)
	end

	-- Close the socket
	socket:close()

	local status, result = p2p_parse(response)

	if(status == false) then
		return false, "Data received, but wasn't Conficker data: " .. result
	end

	if(result['hash'] ~= result['real_hash']) then
		return false, "Data received, but checksum was invalid (possibly INFECTED)"
	end

	return true, "Received valid data", result
end

action = function(host)
	local tcp_ports = {}
	local udp_ports = {}
	local response = {}
	local i
	local port, protocol
	local count = 0
	local checks = 0

	-- Generate a complete list of valid ports
	if(nmap.registry.args.checkall == "true" or nmap.registry.args.checkall == "1") then
		for i = 1, 65535, 1 do
			if(not(is_blacklisted_port(i))) then
				local tcp = nmap.get_port_state(host, {number=i, protocol="tcp"})
				if(tcp ~= nil and tcp.state == "open") then
					tcp_ports[i] = true
				end
	
				local udp = nmap.get_port_state(host, {number=i, protocol="udp"})
				if(udp ~= nil and (udp.state == "open" or udp.state == "open|filtered")) then
					udp_ports[i] = true
				end
			end
		end
	end


	-- Generate ports based on the ip and time
	local seed = math.floor((os.time() - 345600) / 604800)
	local ip = host.ip

	-- Use the provided IP, if it exists
	if(nmap.registry.args.realip ~= nil) then
		ip = nmap.registry.args.realip
	end

	-- Reverse the IP's endianness
	ip = ipOps.todword(ip)
	ip = bin.pack(">I", ip)
	local _
	_, ip = bin.unpack("<I", ip)

	-- Generate the ports
	local generated_ports = prng_generate_ports(ip, seed)
	tcp_ports[generated_ports[1]] = true
	tcp_ports[generated_ports[3]] = true
	udp_ports[generated_ports[2]] = true
	udp_ports[generated_ports[4]] = true

	table.insert(response, string.format("Checking for Conficker.C or higher..."))

	-- Check the TCP ports
	for port in pairs(tcp_ports) do
		local status, reason

		status, reason = conficker_check(host.ip, port, "tcp")
		checks = checks + 1

		if(status == true) then
			table.insert(response, string.format("Check %d (port %d/%s): INFECTED (%s)", checks, port, "tcp", reason))
			count = count + 1
		else
			table.insert(response, string.format("Check %d (port %d/%s): CLEAN (%s)", checks, port, "tcp", reason))
		end
	end

	-- Check the UDP ports
	for port in pairs(udp_ports) do
		local status, reason

		status, reason = conficker_check(host.ip, port, "udp")
		checks = checks + 1

		if(status == true) then
			table.insert(response, string.format("Check %d (port %d/%s): INFECTED (%s)", checks, port, "udp", reason))
			count = count + 1
		else
			table.insert(response, string.format("| Check %d (port %d/%s): CLEAN (%s)", checks, port, "udp", reason))
		end
	end

	-- Check how many INFECTED hits we got
	if(count == 0) then
		if (nmap.verbosity() > 1) then
			table.insert(response, string.format("%d/%d checks are positive: Host is CLEAN or ports are blocked", count, checks))
		else
			response = ''
		end
	else
		table.insert(response, string.format("%d/%d checks are positive: Host is likely INFECTED", count, checks))
	end

	return stdnse.format_output(true, response)
end

