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14 <title>HTML Purifier - Filter your HTML the standards-compliant way!
</title>
15 <xi:include href=
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16 <meta name=
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17 content=
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19 content=
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28 type=
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29 title=
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35 <span class=
"html">HTML
</span>
36 <span class=
"purifier">Purifier
</span>
40 Standards-Compliant HTML Filtering
45 <xi:include href=
"common-navigation.xml" xpointer=
"xpointer(/*/node())" />
51 <div id=
"summary-safe">
54 HTML Purifier defeats XSS with an audited whitelist
57 <div id=
"summary-clean">
60 HTML Purifier ensures standards-compliant output
63 <div id=
"summary-open">
66 HTML Purifier is open-source and highly customizable
72 <p><strong>HTML Purifier
</strong> is a standards-compliant
73 <abbr>HTML
</abbr> filter library written in
74 <abbr>PHP
</abbr>. HTML Purifier will not only remove all malicious
75 code (better known as
<abbr>XSS
</abbr>) with a thoroughly audited,
76 secure
<em>yet
</em> permissive
<strong><a
77 href=
"live/smoketests/printDefinition.php">whitelist
</a></strong>,
78 it will also make sure your documents are
79 <strong>standards compliant
</strong>, something only achievable with a
80 comprehensive knowledge of
<abbr>W3C
</abbr>'s specifications.
81 Tired of using BBCode due to the current landscape of deficient or
82 insecure
<abbr>HTML
</abbr> filters? Have a
83 <strong><acronym>WYSIWYG
</acronym></strong> editor but never been able to use it? Looking
84 for high-quality, standards-compliant, open-source components for that
85 application you're building? HTML Purifier is for you!
</p>
87 <blockquote class=
"fancy">
89 I'd just like to say we use HTML Purifier in
<a href=
"http://www.iris.ac/">IRIS
</a> for
90 filtering emails against XSS attacks and we've been more than impressed.
92 <div class=
"origin">— Chris Corbyn,
<em>Senior IRIS Developer
</em></div>
95 <xi:include href=
"download-box.xml" xpointer=
"xpointer(/*/node())" />
99 <h2 id=
"Background" class=
"clear">Background
</h2>
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>
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>
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>
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><a
></code> tags cannot be nested
128 within each other!
</p>
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>
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
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
155 <blockquote class=
"fancy">
157 [Y]ou save my day by allowing me not to write another damned HTML parser.
160 — Joseph Halter,
<em>Technical Director at Akira Web
</em>
164 <h2 id=
"Plugins">Plugins
</h2>
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>
171 <li><a href=
"http://www.phorum.org/phorum5/read.php?62,127035">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 <li><a href=
"http://www.mindloop.be/nieuws/nieuwe-ontwikkelingen/htmlpurifier-and-the-codeigniter-framework">CodeIgniter
</a> by Andy Mathijs
</li>
179 <strong>Notice:
</strong>
180 Any plugin provided by a third party has not been vetted by us: use
181 them at your own risk. If you are having a problem with the plugin,
182 please consult the plugin author before asking for help here (we'll
183 be more than happy to help, but it might be a problem with the
184 plugin rather than HTML Purifier.)
187 <blockquote class=
"fancy">
189 This plugin is on top of my favorite list[.] I am going to heavily
190 depend on it since my clients insist on having
<acronym>WYSIWYG
</acronym> and I insist on
191 having pages that validate and are semantically sound.
194 — David Molliere,
<em>MODx Marketing
& Design Team
</em>
198 <p>Plugins for other major applications gladly accepted!
</p>
202 <h2 id=
"Propaganda">Spread the Word!
</h2>
204 <p>Help spread awareness about HTML Purifier by:
</p>
208 href=
"http://del.icio.us/post?v=4&noui&url=http://htmlpurifier.org/&title=HTML%20Purifier%20-%20Filter%20your%20HTML%20the%20standards-compliant%20way!"
209 id=
"delicious">Bookmarking this website
</a> on your
<strong>del.icio.us
</strong> account, and/or
</li>
211 <div>Including this little
<strong>label
</strong> on your website:
212 <a href=
"http://htmlpurifier.org/"><img
213 src=
"live/art/powered.png"
214 alt=
"Powered by HTML Purifier" border=
"0" /></a>, with this code:
216 <pre class=
"long"><a href=
"http://htmlpurifier.org/
"><img
217 src=
"http://htmlpurifier.org/live/art/powered.png
"
218 alt=
"Powered by HTML Purifier
" border=
"0" /
></a
></pre>