ikiwiki/doc/plugins/htmlscrubber.mdwn

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[[!template id=plugin name=htmlscrubber core=1 author="[[Joey]]"]]
[[!tag type/html]]
This plugin is enabled by default. It sanitizes the html on pages it renders
to avoid XSS attacks and the like.
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It excludes all html tags and attributes except for those that are
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whitelisted using the same lists as used by Mark Pilgrim's Universal Feed
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Parser, documented at
<http://web.archive.org/web/20110726052341/http://feedparser.org/docs/html-sanitization.html>.
Notably it strips `style` and `link` tags, and the `style` attribute.
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Any attributes that could be used to specify a URL are checked to ensure
that they are known, safe schemes. It will also block embedded javascript
in such URLs.
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It uses the [[!cpan HTML::Scrubber]] perl module to perform its html
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sanitisation, and this perl module also deals with various entity encoding
tricks.
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While I believe that this makes ikiwiki as resistant to malicious html
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content as anything else on the web, I cannot guarantee that it will
actually protect every user of every browser from every browser security
hole, badly designed feature, etc. I can provide NO WARRANTY, like it says
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in ikiwiki's [[GPL]] license.
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The web's security model is *fundamentally broken*; ikiwiki's html
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sanitisation is only a patch on the underlying gaping hole that is your web
browser.
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Note that enabling or disabling the htmlscrubber plugin also affects some
other HTML-related functionality, such as whether [[meta]] allows
potentially unsafe HTML tags.
The `htmlscrubber_skip` configuration setting can be used to skip scrubbing
of some pages. Set it to a [[ikiwiki/PageSpec]], such as
`posts/* and !comment(*) and !*/Discussion`, and pages matching that can have
all the evil CSS, JavsScript, and unsafe html elements you like. One safe
way to use this is to use [[lockedit]] to lock those pages, so only admins
can edit them.
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----
Some examples of embedded javascript that won't be let through when this
plugin is active:
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* script tag test <script>window.location='http://example.org';</script>
* <span style="background: url(javascript:window.location='http://example.org/')">CSS script test</span>
* <span style="&#x61;&#x6e;&#x79;&#x3a;&#x20;&#x65;&#x78;&#x70;&#x72;&#x65;&#x73;&#x73;&#x69;&#x6f;&#x6e;&#x28;&#x77;&#x69;&#x6e;&#x64;&#x6f;&#x77;&#x2e;&#x6c;&#x6f;&#x63;&#x61;&#x74;&#x69;&#x6f;&#x6e;&#x3d;&#x27;&#x68;&#x74;&#x74;&#x70;&#x3a;&#x2f;&#x2f;&#x65;&#x78;&#x61;&#x6d;&#x70;&#x6c;&#x65;&#x2e;&#x6f;&#x72;&#x67;&#x2f;&#x27;&#x29;">entity-encoded CSS script test</span>
* <span style="&#97;&#110;&#121;&#58;&#32;&#101;&#120;&#112;&#114;&#101;&#115;&#115;&#105;&#111;&#110;&#40;&#119;&#105;&#110;&#100;&#111;&#119;&#46;&#108;&#111;&#99;&#97;&#116;&#105;&#111;&#110;&#61;&#39;&#104;&#116;&#116;&#112;&#58;&#47;&#47;&#101;&#120;&#97;&#109;&#112;&#108;&#101;&#46;&#111;&#114;&#103;&#47;&#39;&#41;">entity-encoded CSS script test</span>
* <a href="javascript&#x3A;alert('foo')">click me</a>