514 lines
14 KiB
Ruby
514 lines
14 KiB
Ruby
# -*- coding: binary -*-
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require 'rex/text'
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require 'rex/random_identifier_generator'
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require 'rkelly'
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module Rex
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module Exploitation
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#
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# Obfuscate JavaScript by randomizing as much as possible and removing
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# easily-signaturable string constants.
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#
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# Example:
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# js = ::Rex::Exploitation::JSObfu.new %Q|
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# var a = "0\\612\\063\\x34\\x35\\x36\\x37\\x38\\u0039";
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# var b = { foo : "foo", bar : "bar" }
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# alert(a);
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# alert(b.foo);
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# |
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# js.obfuscate
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# puts js
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# Example Output:
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# var VwxvESbCgv = String.fromCharCode(0x30,0x31,062,063,064,53,0x36,067,070,0x39);
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# var ToWZPn = {
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# "\146\157\x6f": (function () { var yDyv="o",YnCL="o",Qcsa="f"; return Qcsa+YnCL+yDyv })(),
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# "\142ar": String.fromCharCode(0142,97,0162)
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# };
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# alert(VwxvESbCgv);
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# alert(ToWZPn.foo);
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#
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# NOTE: Variables MUST be declared with a 'var' statement BEFORE first use (or
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# not at all) for this to generate correct code! If variables are not declared
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# they will not be randomized but the generated code will be correct.
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#
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# Bad Example Javascript:
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# a = "asdf"; // this variable hasn't been declared and will not be randomized
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# var a;
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# alert(a); // real js engines will alert "asdf" here
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# Bad Example Obfuscated:
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# a = (function () { var hpHu="f",oyTm="asd"; return oyTm+hpHu })();
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# var zSrnHpEfJZtg;
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# alert(zSrnHpEfJZtg);
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# Notice that the first usage of +a+ (before it was declared) is not
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# randomized. Thus, the obfuscated version will alert 'undefined' instead of
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# "asdf".
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#
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class JSObfu
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# these keywords should never be used as a random var name
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# source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Reserved_Words
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RESERVED_KEYWORDS = %w(
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break case catch continue debugger default delete do else finally
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for function if in instanceof new return switch this throw try
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typeof var void while with class enum export extends import super
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implements interface let package private protected public static yield
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)
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#
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# Abstract Syntax Tree generated by RKelly::Parser#parse
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#
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attr_reader :ast
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#
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# Saves +code+ for later obfuscation with #obfuscate
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#
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def initialize(code)
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@code = code
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@funcs = {}
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@vars = {}
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@debug = false
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@rand_gen = Rex::RandomIdentifierGenerator.new(
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:max_length => 15,
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:first_char_set => Rex::Text::Alpha+"_$",
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:char_set => Rex::Text::AlphaNumeric+"_$"
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)
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end
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#
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# Add +str+ to the un-obfuscated code.
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#
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# Calling this method after #obfuscate is undefined
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#
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def <<(str)
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@code << str
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end
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#
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# Return the (possibly obfuscated) code as a string.
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#
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# If #obfuscate has not been called before this, returns the parsed,
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# unobfuscated code. This can be useful for example to remove comments and
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# standardize spacing.
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#
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def to_s
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parse if not @ast
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@ast.to_ecma
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end
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#
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# Return the obfuscated name of a symbol
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#
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# You MUST call #obfuscate before this method!
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#
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def sym(lookup)
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if @vars[lookup]
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ret = @vars[lookup]
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elsif @funcs[lookup]
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ret = @funcs[lookup]
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else
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ret = lookup
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end
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ret
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end
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#
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# Parse and obfuscate
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#
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def obfuscate
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parse
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obfuscate_r(@ast)
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end
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# @return [String] a unique random var name that is not a reserved keyword
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def random_var_name
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loop do
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text = random_string
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unless @vars.has_value?(text) or RESERVED_KEYWORDS.include?(text)
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return text
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end
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end
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end
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protected
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# @return [String] a random string
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def random_string
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@rand_gen.generate
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end
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#
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# Recursive method to obfuscate the given +ast+.
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#
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# +ast+ should be the result of RKelly::Parser#parse
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#
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def obfuscate_r(ast)
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ast.each do |node|
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#if node.respond_to? :value and node.value.kind_of? String and node.value =~ /bodyOnLoad/i
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# $stdout.puts("bodyOnLoad: #{node.class}: #{node.value}")
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#end
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case node
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when nil
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nil
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when ::RKelly::Nodes::SourceElementsNode
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# Recurse
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obfuscate_r(node.value)
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#when ::RKelly::Nodes::ObjectLiteralNode
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# TODO
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#$stdout.puts(node.methods - Object.new.methods)
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#$stdout.puts(node.value.inspect)
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when ::RKelly::Nodes::PropertyNode
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# Property names must be bare words or string literals NOT
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# expressions! Can't use transform_string() here
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if node.name =~ /^[a-zA-Z_][a-zA-Z0-9_]*$/
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n = '"'
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node.name.unpack("C*") { |c|
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case rand(3)
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when 0; n << "\\x%02x"%(c)
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when 1; n << "\\#{c.to_s 8}"
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when 2; n << [c].pack("C")
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end
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}
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n << '"'
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node.name = n
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end
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# Variables
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when ::RKelly::Nodes::VarDeclNode
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if @vars[node.name].nil?
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@vars[node.name] = random_var_name
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end
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node.name = @vars[node.name]
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when ::RKelly::Nodes::ParameterNode
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if @vars[node.value].nil?
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@vars[node.value] = random_var_name
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end
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node.value = @vars[node.value]
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when ::RKelly::Nodes::ResolveNode
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#$stdout.puts("Resolve bodyOnload: #{@vars[node.value]}") if "bodyOnLoad" == node.value
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node.value = @vars[node.value] if @vars[node.value]
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when ::RKelly::Nodes::DotAccessorNode
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case node.value
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when ::RKelly::Nodes::ResolveNode
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if @vars[node.value.value]
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node.value.value = @vars[node.value.value]
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end
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#else
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# $stderr.puts("Non-resolve node as target of dotaccessor: #{node.value.class}")
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end
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# Functions
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when ::RKelly::Nodes::FunctionDeclNode
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#$stdout.puts("FunctionDecl: #{node.value}")
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# Functions can also act as objects, so store them in the vars
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# and the functions list so we can replace them in both places
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if @funcs[node.value].nil? and not @funcs.values.include?(node.value)
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@funcs[node.value] = random_var_name
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if @vars[node.value].nil?
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@vars[node.value] = @funcs[node.value]
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end
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node.value = @funcs[node.value]
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end
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when ::RKelly::Nodes::FunctionCallNode
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# The value of a FunctionCallNode is some sort of accessor node or a ResolveNode
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# so this is basically useless
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#$stdout.puts("Function call: #{node.name} => #{@funcs[node.name]}")
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#node.value = @funcs[node.value] if @funcs[node.value]
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# Transformers
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when ::RKelly::Nodes::NumberNode
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node.value = transform_number(node.value)
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when ::RKelly::Nodes::StringNode
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node.value = transform_string(node.value)
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else
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#$stderr.puts "#{node.class}: #{node.value}"
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#$stderr.puts "#{node.class}"
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end
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#unless node.kind_of? ::RKelly::Nodes::SourceElementsNode
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# $stderr.puts "#{node.class}: #{node.value}"
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#end
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end
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nil
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end
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#
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# Generate an Abstract Syntax Tree (#ast) for later obfuscation
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#
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def parse
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parser = RKelly::Parser.new
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@ast = parser.parse(@code)
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end
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#
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# Convert a number to a random base (decimal, octal, or hexedecimal).
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#
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# Given 10 as input, the possible return values are:
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# "10"
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# "0xa"
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# "012"
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#
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def rand_base(num)
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case rand(3)
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when 0; num.to_s
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when 1; "0%o" % num
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when 2; "0x%x" % num
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end
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end
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#
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# Return a mathematical expression that will evaluate to the given number
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# +num+.
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#
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# +num+ can be a float or an int, but should never be negative.
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#
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def transform_number(num)
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case num
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when Fixnum
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if num == 0
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r = rand(10) + 1
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transformed = "('#{Rex::Text.rand_text_alpha(r)}'.length - #{r})"
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elsif num > 0 and num < 10
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# use a random string.length for small numbers
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transformed = "'#{Rex::Text.rand_text_alpha(num)}'.length"
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else
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transformed = "("
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divisor = rand(num) + 1
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a = num / divisor.to_i
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b = num - (a * divisor)
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# recurse half the time for a
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a = (rand(2) == 0) ? transform_number(a) : rand_base(a)
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# recurse half the time for divisor
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divisor = (rand(2) == 0) ? transform_number(divisor) : rand_base(divisor)
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transformed << "#{a}*#{divisor}"
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transformed << "+#{b}"
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transformed << ")"
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end
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when Float
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transformed = "(#{num - num.floor} + #{rand_base(num.floor)})"
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end
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#puts("#{num} == #{transformed}")
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transformed
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end
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#
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# Convert a javascript string into something that will generate that string.
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#
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# Randomly calls one of the +transform_string_*+ methods
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#
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def transform_string(str)
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quote = str[0,1]
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# pull off the quotes
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str = str[1,str.length - 2]
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return quote*2 if str.length == 0
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case rand(2)
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when 0
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transformed = transform_string_split_concat(str, quote)
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when 1
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transformed = transform_string_fromCharCode(str)
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#when 2
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# # Currently no-op
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# transformed = transform_string_unescape(str)
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end
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#$stderr.puts "Obfuscating str: #{str.ljust 30} #{transformed}"
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transformed
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end
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#
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# Split a javascript string, +str+, without breaking escape sequences.
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#
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# The maximum length of each piece of the string is half the total length
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# of the string, ensuring we (almost) always split into at least two
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# pieces. This won't always be true when given a string like "AA\x41",
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# where escape sequences artificially increase the total length (escape
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# sequences are considered a single character).
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#
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# Returns an array of two-element arrays. The zeroeth element is a
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# randomly generated variable name, the first is a piece of the string
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# contained in +quote+s.
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#
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# See #escape_length
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#
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def safe_split(str, quote)
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parts = []
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max_len = str.length / 2
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while str.length > 0
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len = 0
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loop do
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e_len = escape_length(str[len..-1])
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e_len = 1 if e_len.nil?
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len += e_len
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# if we've reached the end of the string, bail
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break unless str[len]
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break if len > max_len
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# randomize the length of each part
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break if (rand(4) == 0)
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end
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part = str.slice!(0, len)
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var = Rex::Text.rand_text_alpha(4)
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parts.push( [ var, "#{quote}#{part}#{quote}" ] )
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end
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parts
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end
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#
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# Stolen from obfuscatejs.rb
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#
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# Determines the length of an escape sequence
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#
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def escape_length(str)
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esc_len = nil
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if str[0,1] == "\\"
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case str[1,1]
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when "u"; esc_len = 6 # unicode \u1234
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when "x"; esc_len = 4 # hex, \x41
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when /[0-7]/ # octal, \123, \0
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str[1,3] =~ /([0-7]{1,3})/
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if $1.to_i(8) > 255
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str[1,3] =~ /([0-7]{1,2})/
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end
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esc_len = 1 + $1.length
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else; esc_len = 2 # \" \n, etc.
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end
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end
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esc_len
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end
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#
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# Split a javascript string, +str+, into multiple randomly-ordered parts
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# and return an anonymous javascript function that joins them in the
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# correct order. This method can be called safely on strings containing
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# escape sequences. See #safe_split.
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#
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def transform_string_split_concat(str, quote)
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parts = safe_split(str, quote)
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func = "(function () { var "
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ret = "; return "
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parts.sort { |a,b| rand }.each do |part|
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func << "#{part[0]}=#{part[1]},"
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end
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func.chop!
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ret << parts.map{|part| part[0]}.join("+")
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final = func + ret + " })()"
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final
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end
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# TODO
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#def transform_string_unescape(str)
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# str
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#end
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#
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# Return a call to String.fromCharCode() with each char of the input as arguments
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#
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# Example:
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# input : "A\n"
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# output: String.fromCharCode(0x41, 10)
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#
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def transform_string_fromCharCode(str)
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buf = "String.fromCharCode("
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bytes = str.unpack("C*")
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len = 0
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while str.length > 0
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if str[0,1] == "\\"
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str.slice!(0,1)
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# then this is an escape sequence and we need to deal with all
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# the special cases
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case str[0,1]
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# For chars that contain their non-escaped selves, step past
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# the backslash and let the rand_base() below decide how to
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# represent the character.
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when '"', "'", "\\", " "
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char = str.slice!(0,1).unpack("C").first
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# For symbolic escapes, use the known value
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when "n"; char = 0x0a; str.slice!(0,1)
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when "t"; char = 0x09; str.slice!(0,1)
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# Lastly, if it's a hex, unicode, or octal escape, pull out the
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# real value and use that
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when "x"
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# Strip the x
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str.slice!(0,1)
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char = str.slice!(0,2).to_i 16
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when "u"
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# This can potentially lose information in the case of
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# characters like \u0041, but since regular ascii is stored
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# as unicode internally, String.fromCharCode(0x41) will be
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# represented as 00 41 in memory anyway, so it shouldn't
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# matter.
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str.slice!(0,1)
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char = str.slice!(0,4).to_i 16
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when /[0-7]/
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# Octals are a bit harder since they are variable width and
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# don't necessarily mean what you might think. For example,
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# "\61" == "1" and "\610" == "10". 610 is a valid octal
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# number, but not a valid ascii character. Javascript will
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# interpreter as much as it can as a char and use the rest
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# as a literal. Boo.
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str =~ /([0-7]{1,3})/
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char = $1.to_i 8
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if char > 255
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str =~ /([0-7]{1,2})/
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char = $1.to_i 8
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end
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str.slice!(0,$1.length)
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end
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else
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char = str.slice!(0,1).unpack("C").first
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end
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buf << "#{rand_base(char)},"
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end
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# Strip off the last comma
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buf = buf[0,buf.length-1] + ")"
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transformed = buf
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transformed
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end
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end
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end
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end
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=begin
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if __FILE__ == $0
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if ARGV[0]
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code = File.read(ARGV[0])
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else
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#require 'rex/exploitation/javascriptosdetect'
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#code = Rex::Exploitation::JavascriptOSDetect.new.to_s
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code = <<-EOS
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// Should alert "0123456789"
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var a = "0\\612\\063\\x34\\x35\\x36\\x37\\x38\\u0039";
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var a,b=2,c=3;
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alert(a);
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// should alert "asdfjkl;"
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var d = (function() { var foo = "jkl;", blah = "asdf"; return blah + foo; })();
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alert(d);
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EOS
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end
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js = Rex::Exploitation::JSObfu.new(code)
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js.obfuscate
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puts js.to_s
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end
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=end
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