handle nested script tags

proposed fix for #127

lib/loofah/scrubbers.rb

@@ -99,7 +99,12 @@ def initialize
 
       def scrub(node)
         return CONTINUE if html5lib_sanitize(node) == CONTINUE
-        node.before node.children
+        if node.children.length == 1 && node.children.first.cdata?
+          sanitized_text = Loofah.fragment(node.children.first.to_html).scrub!(:strip).to_html
+          node.before Nokogiri::XML::Text.new(sanitized_text, node.document)
+        else
+          node.before node.children
+        end
         node.remove
       end
     end

test/integration/test_ad_hoc.rb

@@ -157,6 +157,20 @@ def test_return_empty_string_when_nothing_left
       assert_equal "", Loofah.scrub_document('<script>test</script>', :prune).text
     end
 
+    def test_nested_script_cdata_tags_should_be_scrubbed
+      html = "<script><script src='malicious.js'></script>"
+      stripped = Loofah.fragment(html).scrub!(:strip)
+      assert_empty stripped.xpath("//script")
+      refute_match("<script", stripped.to_html)
+    end
+
+    def test_nested_script_cdata_tags_should_be_scrubbed_2
+      html = "<script><script>alert('a');</script></script>"
+      stripped = Loofah.fragment(html).scrub!(:strip)
+      assert_empty stripped.xpath("//script")
+      refute_match("<script", stripped.to_html)
+    end
+
     def test_removal_of_all_tags
       html = <<-HTML
       What's up <strong>doc</strong>?