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> # xhtml_sanitize('Click here for $100') # => Click here for $100 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(//, ">") 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("
#{sanitized}
") sanitized = doc.to_s.gsub(/\A
(.*)<\/div>\Z/m, '\1') rescue REXML::ParseException sanitized = sanitized.escapeHTML end end