Finally! XSS-protection, done right.

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lib/chunks/engines.rb

@@ -23,75 +23,62 @@ module Engines
 
   end
 
-  MY_VERBOTEN_TAGS = %w(form script plaintext object embed applet iframe frameset frame link meta body style html) 
-  MY_VERBOTEN_ATTRS = /^on/i
-
   class Textile < AbstractEngine
-    require_dependency 'action_view/helpers/text_helper'
+    require_dependency 'sanitize'
-    ActionView::Helpers::TextHelper::VERBOTEN_TAGS = MY_VERBOTEN_TAGS
+    include Sanitize
-    ActionView::Helpers::TextHelper::VERBOTEN_ATTRS = MY_VERBOTEN_ATTRS
-    include ActionView::Helpers::TextHelper
     def mask
       require_dependency 'redcloth'
       redcloth = RedCloth.new(@content, [:hard_breaks] + @content.options[:engine_opts])
       redcloth.filter_html = false
       redcloth.no_span_caps = false  
       html = redcloth.to_html(:textile)
-      sanitize(html)
+      sanitize_html(html)
     end
   end
 
   class Markdown < AbstractEngine
-    require_dependency 'action_view/helpers/text_helper'
+    require_dependency 'sanitize'
-    ActionView::Helpers::TextHelper::VERBOTEN_TAGS = MY_VERBOTEN_TAGS
+    include Sanitize
-    ActionView::Helpers::TextHelper::VERBOTEN_ATTRS = MY_VERBOTEN_ATTRS
-    include ActionView::Helpers::TextHelper
     def mask
       require_dependency 'maruku'
       require_dependency 'maruku/ext/math'
       html = Maruku.new(@content.delete("\r\x01-\x08\x0B\x0C\x0E-\x1F"), {:math_enabled => false}).to_html
-      sanitize(html)
+      sanitize_html(html)
     end
   end
 
   class MarkdownMML < AbstractEngine
-    require_dependency 'action_view/helpers/text_helper'
+    require_dependency 'sanitize'
-    ActionView::Helpers::TextHelper::VERBOTEN_TAGS = MY_VERBOTEN_TAGS
+    include Sanitize
-    ActionView::Helpers::TextHelper::VERBOTEN_ATTRS = MY_VERBOTEN_ATTRS
-    include ActionView::Helpers::TextHelper
     def mask
       require_dependency 'maruku'
       require_dependency 'maruku/ext/math'
       html = Maruku.new(@content.delete("\r\x01-\x08\x0B\x0C\x0E-\x1F"),
             {:math_enabled => true, :math_numbered => ['\\[','\\begin{equation}']}).to_html
-      sanitize(html)
+      sanitize_html(html)
     end
   end
 
   class Mixed < AbstractEngine
-    require_dependency 'action_view/helpers/text_helper'
+    require_dependency 'sanitize'
-    ActionView::Helpers::TextHelper::VERBOTEN_TAGS = MY_VERBOTEN_TAGS
+    include Sanitize
-    ActionView::Helpers::TextHelper::VERBOTEN_ATTRS = MY_VERBOTEN_ATTRS
-    include ActionView::Helpers::TextHelper
     def mask
       require_dependency 'redcloth'
       redcloth = RedCloth.new(@content, @content.options[:engine_opts])
       redcloth.filter_html = false
       redcloth.no_span_caps = false
       html = redcloth.to_html
-      sanitize(html)
+      sanitize_html(html)
     end
   end
 
   class RDoc < AbstractEngine
-    require_dependency 'action_view/helpers/text_helper'
+    require_dependency 'sanitize'
-    ActionView::Helpers::TextHelper::VERBOTEN_TAGS = MY_VERBOTEN_TAGS
+    include Sanitize
-    ActionView::Helpers::TextHelper::VERBOTEN_ATTRS = MY_VERBOTEN_ATTRS
-    include ActionView::Helpers::TextHelper
     def mask
       require_dependency 'rdocsupport'
       html = RDocSupport::RDocFormatter.new(@content).to_html
-      sanitize(html)
+      sanitize_html(html)
     end
   end
 

lib/sanitize.rb

@@ -0,0 +1,188 @@
+module Sanitize
+
+# This module provides sanitization of XHTML+MathML+SVG
+# and of inline style attributes.
+#
+# Based heavily on Sam Ruby's code in the Universal FeedParser.
+
+  acceptable_elements = ['a', 'abbr', 'acronym', 'address', 'area', 'b',
+      'big', 'blockquote', 'br', 'button', 'caption', 'center', 'cite',
+      'code', 'col', 'colgroup', 'dd', 'del', 'dfn', 'dir', 'div', 'dl', 'dt',
+      'em', 'fieldset', 'font', 'form', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
+      'hr', 'i', 'img', 'input', 'ins', 'kbd', 'label', 'legend', 'li', 'map',
+      'menu', 'ol', 'optgroup', 'option', 'p', 'pre', 'q', 's', 'samp',
+      'select', 'small', 'span', 'strike', 'strong', 'sub', 'sup', 'table',
+      'tbody', 'td', 'textarea', 'tfoot', 'th', 'thead', 'tr', 'tt', 'u',
+      'ul', 'var']
+      
+  mathml_elements = ['maction', 'math', 'merror', 'mfrac', 'mi',
+      'mmultiscripts', 'mn', 'mo', 'mover', 'mpadded', 'mphantom',
+      'mprescripts', 'mroot', 'mrow', 'mspace', 'msqrt', 'mstyle', 'msub',
+      'msubsup', 'msup', 'mtable', 'mtd', 'mtext', 'mtr', 'munder',
+      'munderover', 'none']
+      
+  svg_elements = ['a', 'animate', 'animateColor', 'animateMotion',
+      'animateTransform', 'circle', 'defs', 'desc', 'ellipse', 'font-face',
+      'font-face-name', 'font-face-src', 'g', 'glyph', 'hkern', 'image',
+      'linearGradient', 'line', 'metadata', 'missing-glyph', 'mpath', 'path',
+      'polygon', 'polyline', 'radialGradient', 'rect', 'set', 'stop', 'svg',
+      'switch', 'text', 'title', 'use']
+      
+  acceptable_attributes = ['abbr', 'accept', 'accept-charset', 'accesskey',
+      'action', 'align', 'alt', 'axis', 'border', 'cellpadding',
+      'cellspacing', 'char', 'charoff', 'charset', 'checked', 'cite', 'class',
+      'clear', 'cols', 'colspan', 'color', 'compact', 'coords', 'datetime',
+      'dir', 'disabled', 'enctype', 'for', 'frame', 'headers', 'height',
+      'href', 'hreflang', 'hspace', 'id', 'ismap', 'label', 'lang',
+      'longdesc', 'maxlength', 'media', 'method', 'multiple', 'name',
+      'nohref', 'noshade', 'nowrap', 'prompt', 'readonly', 'rel', 'rev',
+      'rows', 'rowspan', 'rules', 'scope', 'selected', 'shape', 'size',
+      'span', 'src', 'start', 'style', 'summary', 'tabindex', 'target', 'title',
+      'type', 'usemap', 'valign', 'value', 'vspace', 'width', 'xml:lang']
+
+
+  mathml_attributes = ['actiontype', 'align', 'columnalign', 'columnalign',
+      'columnalign', 'columnlines', 'columnspacing', 'columnspan', 'depth',
+      'display', 'displaystyle', 'equalcolumns', 'equalrows', 'fence',
+      'fontstyle', 'fontweight', 'frame', 'height', 'linethickness', 'lspace',
+      'mathbackground', 'mathcolor', 'mathvariant', 'mathvariant', 'maxsize',
+      'minsize', 'other', 'rowalign', 'rowalign', 'rowalign', 'rowlines',
+      'rowspacing', 'rowspan', 'rspace', 'scriptlevel', 'selection',
+      'separator', 'stretchy', 'width', 'width', 'xlink:href', 'xlink:show',
+      'xlink:type', 'xmlns', 'xmlns:xlink']
+
+      
+  svg_attributes = ['accent-height', 'accumulate', 'additive', 'alphabetic',
+       'arabic-form', 'ascent', 'attributeName', 'attributeType',
+       'baseProfile', 'bbox', 'begin', 'by', 'calcMode', 'cap-height',
+       'class', 'color', 'color-rendering', 'content', 'cx', 'cy', 'd',
+       'descent', 'display', 'dur', 'end', 'fill', 'fill-rule', 'font-family',
+       'font-size', 'font-stretch', 'font-style', 'font-variant',
+       'font-weight', 'from', 'fx', 'fy', 'g1', 'g2', 'glyph-name', 
+       'gradientUnits', 'hanging', 'height', 'horiz-adv-x', 'horiz-origin-x',
+       'id', 'ideographic', 'k', 'keyPoints', 'keySplines', 'keyTimes',
+       'lang', 'mathematical', 'max', 'min', 'name', 'offset', 'opacity',
+       'origin', 'overline-position', 'overline-thickness', 'panose-1',
+       'path', 'pathLength', 'points', 'preserveAspectRatio', 'r',
+       'repeatCount', 'repeatDur', 'requiredExtensions', 'requiredFeatures',
+       'restart', 'rotate', 'rx', 'ry', 'slope', 'stemh', 'stemv', 
+       'stop-color', 'stop-opacity', 'strikethrough-position',
+       'strikethrough-thickness', 'stroke', 'stroke-dasharray',
+       'stroke-dashoffset', 'stroke-linecap', 'stroke-linejoin',
+       'stroke-miterlimit', 'stroke-width', 'systemLanguage', 'target',
+       'text-anchor', 'to', 'transform', 'type', 'u1', 'u2',
+       'underline-position', 'underline-thickness', 'unicode',
+       'unicode-range', 'units-per-em', 'values', 'version', 'viewBox',
+       'visibility', 'width', 'widths', 'x', 'x-height', 'x1', 'x2',
+       'xlink:actuate', 'xlink:arcrole', 'xlink:href', 'xlink:role',
+       'xlink:show', 'xlink:title', 'xlink:type', 'xml:base', 'xml:lang',
+       'xml:space', 'xmlns', 'xmlns:xlink', 'y', 'y1', 'y2', 'zoomAndPan']
+
+  acceptable_css_properties = ['azimuth', 'background-color',
+      'border-bottom-color', 'border-collapse', 'border-color',
+      'border-left-color', 'border-right-color', 'border-top-color', 'clear',
+      'color', 'cursor', 'direction', 'display', 'elevation', 'float', 'font',
+      'font-family', 'font-size', 'font-style', 'font-variant', 'font-weight',
+      'height', 'letter-spacing', 'line-height', 'overflow', 'pause',
+      'pause-after', 'pause-before', 'pitch', 'pitch-range', 'richness',
+      'speak', 'speak-header', 'speak-numeral', 'speak-punctuation',
+      'speech-rate', 'stress', 'text-align', 'text-decoration', 'text-indent',
+      'unicode-bidi', 'vertical-align', 'voice-family', 'volume',
+      'white-space', 'width']
+
+  acceptable_css_keywords = ['auto', 'aqua', 'black', 'block', 'blue',
+      'bold', 'both', 'bottom', 'brown', 'center', 'collapse', 'dashed',
+      'dotted', 'fuchsia', 'gray', 'green', '!important', 'italic', 'left',
+      'lime', 'maroon', 'medium', 'none', 'navy', 'normal', 'nowrap', 'olive',
+      'pointer', 'purple', 'red', 'right', 'solid', 'silver', 'teal', 'top',
+      'transparent', 'underline', 'white', 'yellow']
+
+  acceptable_svg_properties = [ 'fill', 'fill-opacity', 'fill-rule',
+      'stroke', 'stroke-width', 'stroke-linecap', 'stroke-linejoin',
+      'stroke-opacity']
+
+      ALLOWED_ELEMENTS = acceptable_elements + mathml_elements + svg_elements  unless defined?(ALLOWED_ELEMENTS)
+      ALLOWED_ATTRIBUTES = acceptable_attributes + mathml_attributes + svg_attributes unless defined?(ALLOWED_ATTRIBUTES)
+      ALLOWED_CSS_PROPERTIES = acceptable_css_properties unless defined?(ALLOWED_CSS_PROPERTIES)
+      ALLOWED_CSS_KEYWORDS = acceptable_css_keywords unless defined?(ALLOWED_CSS_KEYWORDS)
+      ALLOWED_SVG_PROPERTIES = acceptable_svg_properties unless defined?(ALLOWED_SVG_PROPERTIES)
+
+      # Sanitize the +html+, escaping all elements not in ALLOWED_ELEMENTS, and stripping out all
+      # attributes not in ALLOWED_ATTRIBUTES. Style attributes are parsed, and a restricted set,
+      # specified by ALLOWED_CSS_PROPERTIES and ALLOWED_CSS_KEYWORDS, are allowed through.
+      # You can adjust what gets sanitized, by defining these constant arrays before this Module is loaded. 
+      #
+      #   sanitize_html('<script> do_nasty_stuff() </script>')
+      #    => &lt;script> do_nasty_stuff() &lt;/script>
+      #   sanitize_html('<a href="javascript: sucker();">Click here for $100</a>')
+      #    => <a>Click here for $100</a>
+      def sanitize_html(html)
+        if html.index("<")
+          tokenizer = HTML::Tokenizer.new(html)
+          new_text = ""
+
+          while token = tokenizer.next
+            node = HTML::Node.parse(nil, 0, 0, token, false)
+            new_text << case node
+              when HTML::Tag
+                if ALLOWED_ELEMENTS.include?(node.name)
+                  if node.closing != :close
+                    node.attributes.delete_if { |attr,v| !ALLOWED_ATTRIBUTES.include?(attr) }
+                    %w(href src).each do |attr|
+                      node.attributes.delete attr if node.attributes[attr] =~ /^\s*javascript:/i
+                    end
+                    if node.attributes['style']
+                      node.attributes['style'] = sanitize_css(node.attributes['style']) 
+                    end
+                  end
+                  node.to_s
+                else
+                  node.to_s.gsub(/</, "&lt;")
+                end
+              else
+                node.to_s.gsub(/</, "&lt;")
+            end
+          end
+
+          html = new_text
+        end
+        html
+      end
+      
+      def sanitize_css(style)
+          # disallow urls
+          style = style.to_s.gsub(/url\s*\(\s*[^\s)]+?\s*\)\s*/, ' ')
+
+          # gauntlet
+          if style !~ /^([:,;#%.\sa-zA-Z0-9!]|\w-\w|\'[\s\w]+\'|\"[\s\w]+\"|\([\d,\s]+\))*$/
+             style = ''
+             return style
+          end
+          if style !~ /^(\s*[-\w]+\s*:\s*[^:;]*(;|$))*$/
+             style = ''
+             return style
+          end
+
+          clean = []
+          style.scan(/([-\w]+)\s*:\s*([^:;]*)/) do |prop,val|
+            if ALLOWED_CSS_PROPERTIES.include?(prop.downcase)
+              clean <<  prop + ': ' + val + ';'
+            elsif ['background','border','margin','padding'].include?(prop.split('-')[0].downcase) 
+              goodval = true
+              val.split().each do |keyword|
+                if !ALLOWED_CSS_KEYWORDS.include?(keyword) and 
+                    keyword !~ /^(#[0-9a-f]+|rgb\(\d+%?,\d*%?,?\d*%?\)?|\d{0,2}\.?\d{0,2}(cm|em|ex|in|mm|pc|pt|px|%|,|\))?)$/
+                  goodval = false
+                end
+              end
+              if goodval 
+                clean <<  prop + ': ' + val + ';'
+              end
+            elsif ALLOWED_SVG_PROPERTIES.include?(prop.downcase)
+               clean <<  prop + ': ' + val + ';'
+            end
+          end
+
+          style = clean.join(' ')
+      end
+end