Program: CWE-79
Project: CVE-2018-3741
Buggy source:
module Rails
  module Html
    # === Rails::Html::PermitScrubber
    #
    # Rails::Html::PermitScrubber allows you to permit only your own tags and/or attributes.
    #
    # Rails::Html::PermitScrubber can be subclassed to determine:
    # - When a node should be skipped via +skip_node?+.
    # - When a node is allowed via +allowed_node?+.
    # - When an attribute should be scrubbed via +scrub_attribute?+.
    #
    # Subclasses don't need to worry if tags or attributes are set or not.
    # If tags or attributes are not set, Loofah's behavior will be used.
    # If you override +allowed_node?+ and no tags are set, it will not be called.
    # Instead Loofahs behavior will be used.
    # Likewise for +scrub_attribute?+ and attributes respectively.
    #
    # Text and CDATA nodes are skipped by default.
    # Unallowed elements will be stripped, i.e. element is removed but its subtree kept.
    # Supplied tags and attributes should be Enumerables.
    #
    # +tags=+
    # If set, elements excluded will be stripped.
    # If not, elements are stripped based on Loofahs +HTML5::Scrub.allowed_element?+.
    #
    # +attributes=+
    # If set, attributes excluded will be removed.
    # If not, attributes are removed based on Loofahs +HTML5::Scrub.scrub_attributes+.
    #
    # class CommentScrubber < Html::PermitScrubber
    #   def initialize
    #     super
    #     self.tags = %w(form script comment blockquote)
    #   end
    #
    #   def skip_node?(node)
    #     node.text?
    #   end
    #
    #   def scrub_attribute?(name)
    #     name == "style"
    #   end
    # end
    #
    # See the documentation for Nokogiri::XML::Node to understand what's possible
    # with nodes: http://nokogiri.org/Nokogiri/XML/Node.html
    class PermitScrubber < Loofah::Scrubber
      attr_reader :tags, :attributes

      def initialize
        @direction = :bottom_up
        @tags, @attributes = nil, nil
      end

      def tags=(tags)
        @tags = validate!(tags, :tags)
      end

      def attributes=(attributes)
        @attributes = validate!(attributes, :attributes)
      end

      def scrub(node)
        if node.cdata?
          text = node.document.create_text_node node.text
          node.replace text
          return CONTINUE
        end
        return CONTINUE if skip_node?(node)

        unless keep_node?(node)
          return STOP if scrub_node(node) == STOP
        end

        scrub_attributes(node)
      end

      protected

      def allowed_node?(node)
        @tags.include?(node.name)
      end

      def skip_node?(node)
        node.text?
      end

      def scrub_attribute?(name)
        !@attributes.include?(name)
      end

      def keep_node?(node)
        if @tags
          allowed_node?(node)
        else
          Loofah::HTML5::Scrub.allowed_element?(node.name)
        end
      end

      def scrub_node(node)
        node.before(node.children) # strip
        node.remove
      end

      def scrub_attributes(node)
        if @attributes
          node.attribute_nodes.each do |attr|
            attr.remove if scrub_attribute?(attr.name)
            scrub_attribute(node, attr)
          end

          scrub_css_attribute(node)
        else
          Loofah::HTML5::Scrub.scrub_attributes(node)
        end
      end

      def scrub_css_attribute(node)
        if Loofah::HTML5::Scrub.respond_to?(:scrub_css_attribute)
          Loofah::HTML5::Scrub.scrub_css_attribute(node)
        else
          style = node.attributes['style']
          style.value = Loofah::HTML5::Scrub.scrub_css(style.value) if style
        end
      end

      def validate!(var, name)
        if var && !var.is_a?(Enumerable)
          raise ArgumentError, "You should pass :#{name} as an Enumerable"
        end
        var
      end

      def scrub_attribute(node, attr_node)
        attr_name = if attr_node.namespace
                      "#{attr_node.namespace.prefix}:#{attr_node.node_name}"
                    else
                      attr_node.node_name
                    end

        if Loofah::HTML5::WhiteList::ATTR_VAL_IS_URI.include?(attr_name)
          # this block lifted nearly verbatim from HTML5 sanitization
          val_unescaped = CGI.unescapeHTML(attr_node.value).gsub(Loofah::HTML5::Scrub::CONTROL_CHARACTERS,'').downcase
          if val_unescaped =~ /^[a-z0-9][-+.a-z0-9]*:/ && ! Loofah::HTML5::WhiteList::ALLOWED_PROTOCOLS.include?(val_unescaped.split(Loofah::HTML5::WhiteList::PROTOCOL_SEPARATOR)[0])
            attr_node.remove
          end
        end
        if Loofah::HTML5::WhiteList::SVG_ATTR_VAL_ALLOWS_REF.include?(attr_name)
          attr_node.value = attr_node.value.gsub(/url\s*\(\s*[^#\s][^)]+?\)/m, ' ') if attr_node.value
        end
        if Loofah::HTML5::WhiteList::SVG_ALLOW_LOCAL_HREF.include?(node.name) && attr_name == 'xlink:href' && attr_node.value =~ /^\s*[^#\s].*/m
          attr_node.remove
        end

        node.remove_attribute(attr_node.name) if attr_name == 'src' && attr_node.value !~ /[^[:space:]]/
      end
    end

    # === Rails::Html::TargetScrubber
    #
    # Where Rails::Html::PermitScrubber picks out tags and attributes to permit in
    # sanitization, Rails::Html::TargetScrubber targets them for removal.
    #
    # +tags=+
    # If set, elements included will be stripped.
    #
    # +attributes=+
    # If set, attributes included will be removed.
    class TargetScrubber < PermitScrubber
      def allowed_node?(node)
        !super
      end

      def scrub_attribute?(name)
        !super
      end
    end

    # === Rails::Html::TextOnlyScrubber
    #
    # Rails::Html::TextOnlyScrubber allows you to permit text nodes.
    #
    # Unallowed elements will be stripped, i.e. element is removed but its subtree kept.
    class TextOnlyScrubber < Loofah::Scrubber
      def initialize
        @direction = :bottom_up
      end

      def scrub(node)
        if node.text?
          CONTINUE
        else
          node.before node.children
          node.remove
        end
      end
    end
  end
end


Fixed version (ground truth):
module Rails
  module Html
    # === Rails::Html::PermitScrubber
    #
    # Rails::Html::PermitScrubber allows you to permit only your own tags and/or attributes.
    #
    # Rails::Html::PermitScrubber can be subclassed to determine:
    # - When a node should be skipped via +skip_node?+.
    # - When a node is allowed via +allowed_node?+.
    # - When an attribute should be scrubbed via +scrub_attribute?+.
    #
    # Subclasses don't need to worry if tags or attributes are set or not.
    # If tags or attributes are not set, Loofah's behavior will be used.
    # If you override +allowed_node?+ and no tags are set, it will not be called.
    # Instead Loofahs behavior will be used.
    # Likewise for +scrub_attribute?+ and attributes respectively.
    #
    # Text and CDATA nodes are skipped by default.
    # Unallowed elements will be stripped, i.e. element is removed but its subtree kept.
    # Supplied tags and attributes should be Enumerables.
    #
    # +tags=+
    # If set, elements excluded will be stripped.
    # If not, elements are stripped based on Loofahs +HTML5::Scrub.allowed_element?+.
    #
    # +attributes=+
    # If set, attributes excluded will be removed.
    # If not, attributes are removed based on Loofahs +HTML5::Scrub.scrub_attributes+.
    #
    # class CommentScrubber < Html::PermitScrubber
    #   def initialize
    #     super
    #     self.tags = %w(form script comment blockquote)
    #   end
    #
    #   def skip_node?(node)
    #     node.text?
    #   end
    #
    #   def scrub_attribute?(name)
    #     name == "style"
    #   end
    # end
    #
    # See the documentation for Nokogiri::XML::Node to understand what's possible
    # with nodes: http://nokogiri.org/Nokogiri/XML/Node.html
    class PermitScrubber < Loofah::Scrubber
      attr_reader :tags, :attributes

      def initialize
        @direction = :bottom_up
        @tags, @attributes = nil, nil
      end

      def tags=(tags)
        @tags = validate!(tags, :tags)
      end

      def attributes=(attributes)
        @attributes = validate!(attributes, :attributes)
      end

      def scrub(node)
        if node.cdata?
          text = node.document.create_text_node node.text
          node.replace text
          return CONTINUE
        end
        return CONTINUE if skip_node?(node)

        unless keep_node?(node)
          return STOP if scrub_node(node) == STOP
        end

        scrub_attributes(node)
      end

      protected

      def allowed_node?(node)
        @tags.include?(node.name)
      end

      def skip_node?(node)
        node.text?
      end

      def scrub_attribute?(name)
        !@attributes.include?(name)
      end

      def keep_node?(node)
        if @tags
          allowed_node?(node)
        else
          Loofah::HTML5::Scrub.allowed_element?(node.name)
        end
      end

      def scrub_node(node)
        node.before(node.children) # strip
        node.remove
      end

      def scrub_attributes(node)
        if @attributes
          node.attribute_nodes.each do |attr|
            attr.remove if scrub_attribute?(attr.name)
            scrub_attribute(node, attr)
          end

          scrub_css_attribute(node)
        else
          Loofah::HTML5::Scrub.scrub_attributes(node)
        end
      end

      def scrub_css_attribute(node)
        if Loofah::HTML5::Scrub.respond_to?(:scrub_css_attribute)
          Loofah::HTML5::Scrub.scrub_css_attribute(node)
        else
          style = node.attributes['style']
          style.value = Loofah::HTML5::Scrub.scrub_css(style.value) if style
        end
      end

      def validate!(var, name)
        if var && !var.is_a?(Enumerable)
          raise ArgumentError, "You should pass :#{name} as an Enumerable"
        end
        var
      end

      def scrub_attribute(node, attr_node)
        attr_name = if attr_node.namespace
                      "#{attr_node.namespace.prefix}:#{attr_node.node_name}"
                    else
                      attr_node.node_name
                    end

        if Loofah::HTML5::WhiteList::ATTR_VAL_IS_URI.include?(attr_name)
          # this block lifted nearly verbatim from HTML5 sanitization
          val_unescaped = CGI.unescapeHTML(attr_node.value).gsub(Loofah::HTML5::Scrub::CONTROL_CHARACTERS,'').downcase
          if val_unescaped =~ /^[a-z0-9][-+.a-z0-9]*:/ && ! Loofah::HTML5::WhiteList::ALLOWED_PROTOCOLS.include?(val_unescaped.split(Loofah::HTML5::WhiteList::PROTOCOL_SEPARATOR)[0])
            attr_node.remove
          end
        end
        if Loofah::HTML5::WhiteList::SVG_ATTR_VAL_ALLOWS_REF.include?(attr_name)
          attr_node.value = attr_node.value.gsub(/url\s*\(\s*[^#\s][^)]+?\)/m, ' ') if attr_node.value
        end
        if Loofah::HTML5::WhiteList::SVG_ALLOW_LOCAL_HREF.include?(node.name) && attr_name == 'xlink:href' && attr_node.value =~ /^\s*[^#\s].*/m
          attr_node.remove
        end

        node.remove_attribute(attr_node.name) if attr_name == 'src' && attr_node.value !~ /[^[:space:]]/

        Loofah::HTML5::Scrub.force_correct_attribute_escaping! node
      end
    end

    # === Rails::Html::TargetScrubber
    #
    # Where Rails::Html::PermitScrubber picks out tags and attributes to permit in
    # sanitization, Rails::Html::TargetScrubber targets them for removal.
    #
    # +tags=+
    # If set, elements included will be stripped.
    #
    # +attributes=+
    # If set, attributes included will be removed.
    class TargetScrubber < PermitScrubber
      def allowed_node?(node)
        !super
      end

      def scrub_attribute?(name)
        !super
      end
    end

    # === Rails::Html::TextOnlyScrubber
    #
    # Rails::Html::TextOnlyScrubber allows you to permit text nodes.
    #
    # Unallowed elements will be stripped, i.e. element is removed but its subtree kept.
    class TextOnlyScrubber < Loofah::Scrubber
      def initialize
        @direction = :bottom_up
      end

      def scrub(node)
        if node.text?
          CONTINUE
        else
          node.before node.children
          node.remove
        end
      end
    end
  end
end