metasploit-framework/lib/rex/exploitation/obfuscatejs.rb

# -*- coding: binary -*-
require 'rex/text'
module Rex
module Exploitation

#
# Obfuscates javascript in various ways
#
class ObfuscateJS
	attr_reader :opts

	#
	# Obfuscates a javascript string.
	#
	# Options are 'Symbols', described below, and 'Strings', a boolean
	# which specifies whether strings within the javascript should be
	# mucked with (defaults to false).
	#
	# The 'Symbols' argument should have the following format:
	#
	#   {
	#      'Variables'  => [ 'var1', ... ],
	#      'Methods'    => [ 'method1', ... ],
	#      'Namespaces' => [ 'n', ... ],
	#      'Classes'    => [ { 'Namespace' => 'n', 'Class' => 'y'}, ... ]
	#   }
	#
	# Make sure you order your methods, classes, and namespaces by most
	# specific to least specific to prevent partial substitution.  For
	# instance, if you have two methods (joe and joeBob), you should place
	# joeBob before joe because it is more specific and will be globally
	# replaced before joe is replaced.
	#
	# A simple example follows:
	#
	# <code>
	# js = ObfuscateJS.new <<ENDJS
	#     function say_hi() {
	#         var foo = "Hello, world";
	#         document.writeln(foo);
	#     }
	# ENDJS
	# js.obfuscate(
	#     'Symbols' => {
	#	       'Variables' => [ 'foo' ],
	#	       'Methods'   => [ 'say_hi' ]
	#	  }
	#     'Strings' => true
	# )
	# </code>
	#
	# which should generate something like the following:
	#
	# <code>
	# function oJaDYRzFOyJVQCOHk() { var cLprVG = "\x48\x65\x6c\x6c\x6f\x2c\x20\x77\x6f\x72\x6c\x64"; document.writeln(cLprVG); }
	# </code>
	#
	# String obfuscation tries to deal with escaped quotes within strings but
	# won't catch things like
	#     "\\"
	# so be careful.
	#
	def self.obfuscate(js, opts = {})
		ObfuscateJS.new(js).obfuscate(opts)
	end

	#
	# Initialize an instance of the obfuscator
	#
	def initialize(js = "", opts = {})
		@js      = js
		@dynsym  = {}
		@opts    = {
			'Symbols' => {
				'Variables'=>[],
				'Methods'=>[],
				'Namespaces'=>[],
				'Classes'=>[]
			},
			'Strings'=>false
		}
		@done = false
		update_opts(opts) if (opts.length > 0)
	end

	def update_opts(opts)
		if (opts.nil? or opts.length < 1)
			return
		end
		if (@opts['Symbols'] && opts['Symbols'])
			['Variables', 'Methods', 'Namespaces', 'Classes'].each { |k|
				if (@opts['Symbols'][k] && opts['Symbols'][k])
					opts['Symbols'][k].each { |s|
						if (not @opts['Symbols'][k].include? s)
							@opts['Symbols'][k].push(s)
						end
					}
				elsif (opts['Symbols'][k])
					@opts['Symbols'][k] = opts['Symbols'][k]
				end
			}
		elsif opts['Symbols']
			@opts['Symbols'] = opts['Symbols']
		end
		@opts['Strings'] ||= opts['Strings']
	end

	#
	# Returns the dynamic symbol associated with the supplied symbol name
	#
	# If obfuscation has not yet been performed (i.e. obfuscate() has not been
	# called), then this method simply returns its argument
	#
	def sym(name)
		@dynsym[name] || name
	end

	#
	# Obfuscates the javascript string passed to the constructor
	#
	def obfuscate(opts = {})
		#return @js if (@done)
		@done = true

		update_opts(opts)

		if (@opts['Strings'])
			obfuscate_strings()

			# Full space randomization does not work for javascript -- despite
			# claims that space is irrelavent, newlines break things.  Instead,
			# use only space (0x20) and tab (0x09).

			#@js.gsub!(/[\x09\x20]+/) { |s|
			#	len = rand(50)+2
			#	set = "\x09\x20"
			#	buf = ''
			#	while (buf.length < len)
			#		buf << set[rand(set.length)].chr
			#	end
			#
			#	buf
			#}
		end

		# Remove our comments
		remove_comments

		# Globally replace symbols
		replace_symbols(@opts['Symbols']) if @opts['Symbols']

		return @js
	end

	#
	# Returns the replaced javascript string
	#
	def to_s
		@js
	end
	alias :to_str :to_s

	def <<(str)
		@js << str
	end
	def +(str)
		@js + str
	end

protected
	attr_accessor :done

	#
	# Get rid of both single-line C++ style comments and multiline C style comments.
	#
	# Note: embedded comments (e.g.: "/*/**/*/") will break this,
	# but they also break real javascript engines so I don't care.
	#
	def remove_comments
		@js.gsub!(%r{\s+//.*$}, '')
		@js.gsub!(%r{/\*.*?\*/}m, '')
	end

	# Replace method, class, and namespace symbols found in the javascript
	# string
	def replace_symbols(symbols)
		taken = { }

		# Generate random symbol names
		[ 'Variables', 'Methods', 'Classes', 'Namespaces' ].each { |symtype|
			next if symbols[symtype].nil?
			symbols[symtype].each { |sym|
				dyn = Rex::Text.rand_text_alpha(rand(32)+1) until dyn and not taken.key?(dyn)

				taken[dyn] = true

				if symtype == 'Classes'
					full_sym = sym['Namespace'] + "." + sym['Class']
					@dynsym[full_sym] = dyn

					@js.gsub!(/#{full_sym}/) { |m|
						sym['Namespace'] + "." + dyn
					}
				else
					@dynsym[sym] = dyn

					@js.gsub!(/#{sym}/, dyn)
				end
			}
		}
	end

	#
	# Change each string into some javascript that will generate that string
	#
	# There are a couple of caveats to using string obfuscation:
	#   * it tries to deal with escaped quotes within strings but won't catch
	#     things like: "\\"
	#   * depending on the random choices, this can easily balloon a short
	#     string up to hundreds of kilobytes if called multiple times.
	# so be careful.
	#
	def obfuscate_strings()
		@js.gsub!(/".*?[^\\]"|'.*?[^\\]'/) { |str|
			buf = ''
			quote = str[0,1]
			# Pull the quotes off either end
			str = str[1, str.length-2]
			case (rand(2))
			# Disable hex encoding for now.  It's just too big a hassle.
			#when 0
			#	# This is where we can run into trouble with generating
			#	# incorrect code.  If we hex encode a string twice, the second
			#	# encoding will generate the first instead of the original
			#	# string.
			#	if str =~ /\\x/
			#		# Always have to remove spaces from strings so the space
			#		# randomization doesn't mess with them.
			#		buf = quote + str.gsub(/ /, '\x20') + quote
			#	else
			#		buf = '"' + Rex::Text.to_hex(str) + '"'
			#	end
			when 0
				#
				# Escape sequences when naively encoded for unescape become a
				# literal backslash instead of the intended meaning.  To avoid
				# that problem, we scan the string for escapes and leave them
				# unmolested.
				#
				buf << 'unescape("'
				bytes = str.unpack("C*")
				c = 0
				while bytes[c]
					if bytes[c].chr == "\\"
						# XXX This is pretty slow.
						esc_len = parse_escape(bytes, c)
						buf << bytes[c, esc_len].map{|a| a.chr}.join
						c += esc_len
						next
					end
					buf << "%%%0.2x"%(bytes[c])
					# Break the string into smaller strings
					if bytes[c+1] and rand(10) == 0
						buf << '" + "'
					end
					c += 1
				end
				buf << '")'
			when 1
				buf = "String.fromCharCode( "
				bytes = str.unpack("C*")
				c = 0
				while bytes[c]
					if bytes[c].chr == "\\"
						case bytes[c+1].chr
						# For chars that contain their non-escaped selves, step
						# past the backslash and let the rand() below decide
						# how to represent the character.
						when '"'; c += 1
						when "'"; c += 1
						when "\\"; c += 1
						# For others, just take the hex representation out of
						# laziness.
						when "n"; buf << "0x0a"; c += 2; next
						when "t"; buf << "0x09"; c += 2; next
						# Lastly, if it's a hex, unicode, or octal escape,
						# leave it, and anything after it, alone.  At some
						# point we may want to parse up to the end of the
						# escapes and encode subsequent non-escape characters.
						# Since this is the lazy way to do it, spaces after an
						# escape sequence will get away unmodified.  To prevent
						# the space randomizer from hosing the string, convert
						# spaces specifically.
						else
							buf = buf[0,buf.length-1] + " )"
							buf << ' + ("' + bytes[c, bytes.length].map{|a| a==0x20 ? '\x20' : a.chr}.join + '" '
							break
						end
					end
					case (rand(3))
					when 0
						buf << " %i,"%(bytes[c])
					when 1
						buf << " 0%o,"%(bytes[c])
					when 2
						buf << " 0x%0.2x,"%(bytes[c])
					end
					c += 1
				end
				# Strip off the last comma
				buf = buf[0,buf.length-1] + " )"
			end
			buf
		}
		@js
	end

	def parse_escape(bytes, offset)
		esc_len = 0
		if bytes[offset].chr == "\\"
			case bytes[offset+1].chr
			when "u"; esc_len = 6     # unicode \u1234
			when "x"; esc_len = 4     # hex, \x41
			when /[0-9]/              # octal, \123, \0
				oct = bytes[offset+1, 4].map{|a|a.chr}.join
				oct =~ /([0-9]+)/
				esc_len = 1 + $1.length
			else; esc_len = 2         # \" \n, etc.
			end
		end
		esc_len
	end
end

end
end