instiki/lib/sanitizer.rb

module Sanitizer

# This module provides sanitization of XHTML+MathML+SVG
# and of inline style attributes.
#
# Based heavily on Sam Ruby's code in the Universal FeedParser.

  require 'action_controller/vendor/html-scanner/html/tokenizer'
  require 'node'
  require 'stringsupport'
  require 'set'

  acceptable_elements = Set.new %w[a abbr acronym address area audio 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 video]
      
  mathml_elements = Set.new %w[annotation annotation-xml maction math merror mfrac
      mfenced mi mmultiscripts mn mo mover mpadded mphantom mprescripts mroot
      mrow mspace msqrt mstyle msub msubsup msup mtable mtd mtext mtr munder
      munderover none semantics]
      
  svg_elements = Set.new %w[a animate animateColor animateMotion animateTransform
      circle clipPath defs desc ellipse font-face font-face-name font-face-src
      foreignObject g glyph hkern linearGradient line marker metadata
      missing-glyph mpath path polygon polyline radialGradient rect set
      stop svg switch text title tspan use]
      
  acceptable_attributes = Set.new %w[abbr accept accept-charset accesskey action
      align alt axis border cellpadding cellspacing char charoff charset
      checked cite class clear cols colspan color compact controls coords datetime
      dir disabled enctype for frame headers height href hreflang hspace id
      ismap label lang longdesc loop maxlength media method multiple name nohref
      noshade nowrap poster 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 = Set.new %w[actiontype align close columnalign columnalign
      columnalign columnlines columnspacing columnspan depth display
      displaystyle encoding equalcolumns equalrows fence fontstyle fontweight
      frame height linethickness lspace mathbackground mathcolor mathvariant
      mathvariant maxsize minsize open other rowalign rowalign rowalign
      rowlines rowspacing rowspan rspace scriptlevel selection separator
      separators stretchy width width xlink:href xlink:show xlink:type xmlns
      xmlns:xlink]

  svg_attributes = Set.new %w[accent-height accumulate additive alphabetic
       arabic-form ascent attributeName attributeType baseProfile bbox begin
       by calcMode cap-height class clip-path clip-rule color color-rendering
       content cx cy d dx dy descent display dur end fill fill-opacity 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 marker-end
       marker-mid marker-start markerHeight markerUnits markerWidth
       mathematical max min name offset opacity orient origin
       overline-position overline-thickness panose-1 path pathLength points
       preserveAspectRatio r refX refY 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-opacity
       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]
       
  attr_val_is_uri = Set.new %w[href src cite action longdesc xlink:href xml:base]
  
  svg_attr_val_allows_ref = Set.new %w[clip-path color-profile cursor fill
      filter marker marker-start marker-mid marker-end mask stroke]

  svg_allow_local_href = Set.new %w[altGlyph animate animateColor animateMotion
      animateTransform cursor feImage filter linearGradient pattern
      radialGradient textpath tref set use]
    
  acceptable_css_properties = Set.new %w[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 = Set.new %w[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 = Set.new %w[fill fill-opacity fill-rule stroke
      stroke-width stroke-linecap stroke-linejoin stroke-opacity]
      
  acceptable_protocols = Set.new %w[ed2k ftp http https irc mailto news gopher nntp
      telnet webcal xmpp callto feed urn aim rsync tag ssh sftp rtsp afs]
      
      SHORTHAND_CSS_PROPERTIES = Set.new %w[background border margin padding]
      VOID_ELEMENTS = Set.new %w[img br hr link meta area base basefont 
                    col frame input isindex param]

      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)
      ALLOWED_PROTOCOLS = acceptable_protocols unless defined?(ALLOWED_PROTOCOLS)
      ATTR_VAL_IS_URI = attr_val_is_uri unless defined?(ATTR_VAL_IS_URI)
      SVG_ATTR_VAL_ALLOWS_REF = svg_attr_val_allows_ref unless defined?(SVG_ATTR_VAL_ALLOWS_REF)
      SVG_ALLOW_LOCAL_HREF = svg_allow_local_href unless defined?(SVG_ALLOW_LOCAL_HREF)

      # 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.
      # Attributes in ATTR_VAL_IS_URI are scanned, and only uri schemes specified in
      # ALLOWED_PROTOCOLS are allowed.
      # Certain SVG attributes (SVG_ATTR_VAL_ALLOWS_REF) may take a url as a value. These are restricted to
      # fragment-id's (in-document references). Certain SVG elements (SVG_ALLOW_LOCAL_HREF) allow href attributes
      # which, again, are restricted to be fragment-id's.
      # 
      # You can adjust what gets sanitized, by defining these constant arrays before this Module is loaded. 
      #
      #   xhtml_sanitize('<script> do_nasty_stuff() </script>')
      #    => &lt;script> do_nasty_stuff() &lt;/script>
      #   xhtml_sanitize('<a href="javascript: sucker();">Click here for $100</a>')
      #    => <a>Click here for $100</a>
      def xhtml_sanitize(html)
        return html unless sanitizeable?(html)
        tokenizer = HTML::Tokenizer.new(html.to_utf8)
        results = []

        while token = tokenizer.next
          node = XHTML::Node.parse(nil, 0, 0, token, false)
          results << case node.tag?
            when true
              if ALLOWED_ELEMENTS.include?(node.name)
                process_attributes_for node
                node.to_s
              else
                node.to_s.gsub(/</, "&lt;").gsub(/>/, "&gt;")
              end
            else
              node.to_s.unescapeHTML.escapeHTML
          end
        end

        results.join
      end

      def sanitizeable?(text)
        !(text.nil? || text.empty? || !text.index("<"))
      end

  protected
  
    def process_attributes_for(node)
      return unless node.attributes
      node.attributes.each do |attr,val|
        if String === val && ALLOWED_ATTRIBUTES.include?(attr)
          val = val.unescapeHTML.escapeHTML
        else
          node.attributes.delete attr; next
        end
        if attr == 'xlink:href' && SVG_ALLOW_LOCAL_HREF.include?(node.name) && val =~ /^\s*[^#\s]/m
          node.attributes.delete attr; next
        end
        if ATTR_VAL_IS_URI.include?(attr)
          val_unescaped = val.unescapeHTML.as_bytes.gsub(/`|[\000-\040\177\s]+|\302[\200-\240]/,'').downcase
          if val_unescaped =~ /^[a-z0-9][-+.a-z0-9]*:/ && !ALLOWED_PROTOCOLS.include?(val_unescaped.split(':')[0]) 
            node.attributes.delete attr; next
          end                        
        end                     
        val = val.to_s.gsub(/url\s*\(\s*[^#\s][^)]+?\)/mi, ' ') if SVG_ATTR_VAL_ALLOWS_REF.include?(attr)
        val = sanitize_css(val) if attr == 'style'
        node.attributes[attr] = val
      end
    end

    def sanitize_css(style)
      # disallow urls
      style = style.to_s.gsub(/url\s*\(\s*[^\s)]+?\s*\)\s*/, ' ')

      # gauntlet
      return '' unless style =~ /^([-:,;#%.\sa-zA-Z0-9!]|\w-\w|\'[\s\w]+\'|\"[\s\w]+\"|\([\d,\s]+\))*$/
      return '' unless style =~ /^\s*([-\w]+\s*:[^:;]*(;\s*|$))*$/

      clean = []
      style.scan(/([-\w]+)\s*:\s*([^:;]*)/) do |prop, val|
        next if val.empty?
        prop.downcase!
        if self.class.const_get("ALLOWED_CSS_PROPERTIES").include?(prop)
          clean << "#{prop}: #{val};"
        elsif self.class.const_get("SHORTHAND_CSS_PROPERTIES").include?(prop.split('-')[0])
          clean << "#{prop}: #{val};" unless val.split().any? do |keyword|
            !self.class.const_get("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|%|,|\))?)$/
          end
        elsif self.class.const_get("ALLOWED_SVG_PROPERTIES").include?(prop)
          clean << "#{prop}: #{val};"
        end
      end

      clean.join(' ')
    end
    
# Sanitize a string, parsed using XHTML parsing rules. Reparse the result to
#    ensure well-formedness. 
#
# :call-seq:
#    safe_sanitize_xhtml(string)                    -> string
#
# Unless otherwise specified, the string is assumed to be utf-8 encoded.
#
# The string returned is utf-8 encoded. If you want, you can use iconv to convert it to some other encoding.
# (REXML trees are always utf-8 encoded.)
  def safe_xhtml_sanitize(html, options = {})
    sanitized = xhtml_sanitize(html.purify)
    doc = REXML::Document.new("<div xmlns='http://www.w3.org/1999/xhtml'>#{sanitized}</div>")
    sanitized = doc.to_s.gsub(/\A<div xmlns='http:\/\/www.w3.org\/1999\/xhtml'>(.*)<\/div>\Z/m, '\1')
    rescue REXML::ParseException
      sanitized = sanitized.escapeHTML
  end 

end