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  14 <title>HTML Purifier - Filter your HTML the standards-compliant way!</title>
  15 <xi:include href="common-meta.xml" xpointer="xpointer(/*/node())" />
  16 <meta name="description"
  17   content="HTML filter that guards against XSS and ensures standards-compliant output." />
  18 <meta name="keywords"
  19   content="HTMLPurifier, HTML Purifier, HTML, filter, filtering, standards, compliant, w3c, XSS, PHP, security, library, open source, LGPL, whitelist" />
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  23 </head>
  24 <body>
  25
  26 <div id="branding">
  27   <h1>
  28     <span class="html">HTML</span>
  29     <span class="purifier">Purifier</span>
  30   </h1>
  31   <blockquote>
  32     <p>
  33       Standards-Compliant HTML Filtering
  34     </p>
  35   </blockquote>
  36 </div>
  37
  38 <xi:include href="common-navigation.xml" xpointer="xpointer(/*/node())" />
  39
  40 <div id="summary">
  41   <h2>Summary</h2>
  42   <div id="summary-safe">
  43     <h3>Safe</h3>
  44     <p>
  45       HTML Purifier defeats XSS with an audited whitelist
  46     </p>
  47   </div>
  48   <div id="summary-clean">
  49     <h3>Clean</h3>
  50     <p>
  51       HTML Purifier ensures standards-compliant output
  52     </p>
  53   </div>
  54   <div id="summary-open">
  55     <h3>Open</h3>
  56     <p>
  57       HTML Purifier is open-source and highly customizable
  58     </p>
  59   </div>
  60 </div>
  61
  62 <div id="intro">
  63   <p><strong>HTML Purifier</strong> is a standards-compliant
  64   <abbr>HTML</abbr> filter library written in
  65   <abbr>PHP</abbr>. HTML Purifier will not only remove all malicious
  66   code (better known as <abbr>XSS</abbr>) with a thoroughly audited,
  67   secure <em>yet</em> permissive <strong><a
  68   href="live/smoketests/printDefinition.php">whitelist</a></strong>,
  69   it will also make sure your documents are
  70   <strong>standards compliant</strong>, something only achievable with a
  71   comprehensive knowledge of <abbr>W3C</abbr>'s specifications.
  72   Tired of using BBCode due to the current landscape of deficient or
  73   insecure <abbr>HTML</abbr> filters? Have a
  74   <strong><acronym>WYSIWYG</acronym></strong> editor but never been able to use it? Looking
  75   for high-quality, standards-compliant, open-source components for that
  76   application you're building? HTML Purifier is for you!</p>
  77
  78   <div class="notice">
  79     <p>
  80       HTML Purifier celebrates its <strong>2.0</strong> release! Read more
  81       about it at <a href="news/2.0.0-released.html">2.0.0 Released</a>.
  82     </p>
  83   </div>
  84
  85   <blockquote class="fancy">
  86   <div class="quote">
  87       I'd just like to say we use HTML Purifier in <a href="http://www.iris.ac/">IRIS</a> for
  88       filtering emails against XSS attacks and we've been more than impressed.
  89   </div>
  90   <div class="origin">&mdash; Chris Corbyn, <em>Senior IRIS Developer</em></div>
  91   </blockquote>
  92
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  94
  95 </div>
  96
  97 <div id="content">
  98
  99 <h2 id="Background">Background</h2>
 100
 101 <p>There are a number of open-source <abbr>HTML</abbr> filtering solutions out
 102 there on the web already
 103 (i.e. <acronym>PEAR</acronym>'s
 104 <a href="http://pear.php.net/package/HTML_Safe">HTML_Safe</a>,
 105 <a href="http://sourceforge.net/projects/kses">kses</a>
 106 and
 107 <a href="http://simon.incutio.com/archive/2003/02/23/safeHtmlChecker">
 108 SafeHtmlChecker.class.php</a>).  What sets HTML Purifier apart from them?
 109 Aren't all of these choices <q>secure</q>?</p>
 110
 111 <p>When it comes to <abbr>HTML</abbr>, <strong>attention to
 112 detail</strong> is key. Does the library demonstrate an in-depth
 113 knowledge of the <abbr>DTD</abbr> that defines
 114 <abbr>HTML</abbr>? Does it perform its filtering off a robust
 115 whitelist rather than a usually out-dated blacklist? Does it go through
 116 the care to check every single attribute in the document for validity?
 117 Does it actually understand tag markup, or pay lip-service with a series
 118 of deficient regexes and str_replace's?</p>
 119
 120 <p>Somewhere along the way, all of HTML Purifier's predecessors fall
 121 flat. HTML_Safe dooms itself to attacks of the future by using a
 122 blacklist. Configurable filters like kses and PHP Input Filter still
 123 cannot validate the contents inside attributes. With all these gaps in
 124 coverage, none of the usual libraries come close to achieving
 125 <strong>standards-compliance</strong>. There is a user-unfriendly,
 126 draconic <abbr>XML</abbr>-based filter called Safe HTML Checker,
 127 but even it forgets that <code>&lt;a&gt;</code> tags cannot be nested
 128 within each other!</p>
 129
 130 <p><strong>Know thy enemy.</strong> Wily hackers have a huge arsenal of
 131 <abbr>XSS</abbr> hidden within the depths of the
 132 <abbr>HTML</abbr> specification. HTML Purifier takes its
 133 effectiveness from the fact that it will decompose the whole document
 134 into tokens, and rigorously process the tokens by removing
 135 non-whitelisted elements, transforming bad practice tags like font into
 136 span, properly checking the nesting of tags and their children and
 137 validating all attributes according to their <abbr>RFC</abbr>s.
 138 HTML Purifier's comprehensive algorithms are complemented by a
 139 <strong>breadth of knowledge</strong>, ensuring that richly formatted
 140 documents pass through unstripped.</p>
 141
 142 <p>To my knowledge, there is nothing else in the wild that offers
 143 protection from <abbr>XSS</abbr>, standards-compliance, and the
 144 corrective processing of poorly formed <abbr>HTML</abbr>
 145 simultaneously. Don't take my word for it though:
 146 do your research. Investigate the other libraries, and decide for
 147 yourself who you would prefer to be the <strong>gatekeeper</strong> to
 148 your system.</p>
 149
 150 <p>To find out more, you can read the
 151 <a href="comparison.html"><strong>Comparison</strong></a>
 152 for a play-by-play analysis of the major filter libraries currently
 153 out there.</p>
 154
 155 <blockquote class="fancy">
 156 <div class="quote">
 157     [Y]ou save my day by allowing me not to write another damned HTML parser.
 158 </div>
 159 <div class="origin">
 160     &mdash; Joseph Halter, <em>Technical Director at Akira Web</em>
 161 </div>
 162 </blockquote>
 163
 164 <h2 id="Plugins">Plugins</h2>
 165
 166 <p>HTML Purifier is a great library to integrate with existing
 167 <abbr>CMS</abbr>es and other applications or <acronym>WYSIWYG</acronym>
 168 editors.  Currently, we have plugins for these applications:</p>
 169
 170 <ul>
 171     <li><a href="http://www.phorum.org/phorum5/read.php?16,122766">Phorum</a> (in use at our very own forums!)</li>
 172     <li><a href="http://htmlpurifier.org/svnroot/htmlpurifier/trunk/plugins/modx.txt">MODx</a></li>
 173     <li><a href="http://bart.motd.be/projects/html-purifier-drupal-module">Drupal</a> by Bart Jansens</li>
 174     <li><a href="http://urbangiraffe.com/plugins/html-purified/">Wordpress</a> by John Godley</li>
 175 </ul>
 176
 177 <p>
 178     <strong>Warning:</strong> It has
 179     come to my attention that some of these plugins may be insecure.
 180     Any plugin provided by a third party has not been vetted by us: use
 181     them at your own risk. I am confident that HTML Purifier works properly,
 182     so any problems should
 183     be resolved with the respective authors of the plugin.
 184 </p>
 185
 186 <blockquote class="fancy">
 187 <div class="quote">
 188     This plugin is on top of my favorite list[.] I am going to heavily
 189     depend on it since my clients insist on having <acronym>WYSIWYG</acronym> and I insist on
 190     having pages that validate and are semantically sound.
 191 </div>
 192 <div class="origin">
 193     &mdash; David Molliere, <em>MODx Marketing &amp; Design Team</em>
 194 </div>
 195 </blockquote>
 196
 197 <p>Plugins for other major applications gladly accepted!</p>
 198
 199
 200
 201 <h2 id="Docs">Documentation</h2>
 202 <ul>
 203     <li><strong><a href="docs/">End-User
 204         Documentation</a></strong> &mdash; In-depth documents on how to get
 205         the most out of HTML Purifier.</li>
 206     <li><a href="http://htmlpurifier.org/phorum/">Support Forum</a> &mdash; Talk about all things
 207         HTML Purifier.</li>
 208     <li><a href="live/smoketests/printDefinition.php">Print
 209         Definition</a> &mdash; If you want to actually see what HTML Purifier's
 210         filtering rules are, look no further than to this page. You can even
 211         experiment with the configuration to see how things respond to different
 212         directives.</li>
 213     <li><a href="live/smoketests/xssAttacks.php"><abbr>XSS</abbr>
 214         Attacks Smoketest</a> &mdash; Tests how well HTML Purifier fares
 215         against RSnake's famous cheatsheet of <abbr>XSS</abbr> attacks.</li>
 216     <li><a href="live/TODO">Roadmap</a>
 217         &mdash; Subject to lots of delays, but it's a glimpse of the future</li>
 218     <li><a href="live/art/">Artwork</a>
 219         &mdash; Extra media goodies.</li>
 220     <li><a href="live/configdoc/plain.html">Configuration
 221         documentation</a> &mdash; See the <code>INSTALL</code> document on how to
 222         configure your HTML Purifier installation.</li>
 223     <li><a href="http://htmlpurifier.org/doxygen/html/">Doxygen-generated
 224         Documentation</a> &mdash; No class left undocumented!  Cross-referenced
 225         code!  A must-read for any prospective HTML Purifier hacker.
 226         (close by, <a href="http://htmlpurifier.org/phpdoc/">PHPDoc-generated
 227         Documentation.</a>)</li>
 228 </ul>
 229
 230 <h2 id="Propaganda">Spread the Word!</h2>
 231
 232 <p>Help spread awareness about HTML Purifier by:</p>
 233
 234 <ul>
 235 <li><a
 236 href="http://del.icio.us/post?v=4&amp;noui&amp;url=http://htmlpurifier.org/&amp;title=HTML%20Purifier%20-%20Filter%20your%20HTML%20the%20standards-compliant%20way!"
 237 id="delicious">Bookmarking this website</a> on your <strong>del.icio.us</strong> account, and/or</li>
 238 <li>
 239     <div>Including this little <strong>label</strong> on your website:
 240     <a href="http://htmlpurifier.org/"><img
 241     src="live/art/powered.png"
 242     alt="Powered by HTML Purifier" border="0" /></a>, with this code:
 243     </div>
 244     <pre class="long">&lt;a href=&quot;http://htmlpurifier.org/&quot;&gt;&lt;img
 245 src=&quot;http://htmlpurifier.org/live/art/powered.png&quot;
 246 alt=&quot;Powered by HTML Purifier&quot; border=&quot;0&quot; /&gt;&lt;/a&gt;</pre>
 247 </li>
 248 </ul>
 249
 250 </div>
 251
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