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104 lines
4.4 KiB
Go
104 lines
4.4 KiB
Go
// Copyright (c) 2014, David Kitchen <david@buro9.com>
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// * Redistributions of source code must retain the above copyright notice, this
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// list of conditions and the following disclaimer.
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//
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// * Redistributions in binary form must reproduce the above copyright notice,
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// this list of conditions and the following disclaimer in the documentation
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// and/or other materials provided with the distribution.
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//
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// * Neither the name of the organisation (Microcosm) nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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/*
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Package bluemonday provides a way of describing a whitelist of HTML elements
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and attributes as a policy, and for that policy to be applied to untrusted
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strings from users that may contain markup. All elements and attributes not on
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the whitelist will be stripped.
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The default bluemonday.UGCPolicy().Sanitize() turns this:
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Hello <STYLE>.XSS{background-image:url("javascript:alert('XSS')");}</STYLE><A CLASS=XSS></A>World
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Into the more harmless:
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Hello World
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And it turns this:
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<a href="javascript:alert('XSS1')" onmouseover="alert('XSS2')">XSS<a>
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Into this:
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XSS
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Whilst still allowing this:
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<a href="http://www.google.com/">
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<img src="https://ssl.gstatic.com/accounts/ui/logo_2x.png"/>
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</a>
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To pass through mostly unaltered (it gained a rel="nofollow"):
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<a href="http://www.google.com/" rel="nofollow">
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<img src="https://ssl.gstatic.com/accounts/ui/logo_2x.png"/>
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</a>
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The primary purpose of bluemonday is to take potentially unsafe user generated
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content (from things like Markdown, HTML WYSIWYG tools, etc) and make it safe
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for you to put on your website.
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It protects sites against XSS (http://en.wikipedia.org/wiki/Cross-site_scripting)
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and other malicious content that a user interface may deliver. There are many
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vectors for an XSS attack (https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet)
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and the safest thing to do is to sanitize user input against a known safe list
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of HTML elements and attributes.
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Note: You should always run bluemonday after any other processing.
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If you use blackfriday (https://github.com/russross/blackfriday) or
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Pandoc (http://johnmacfarlane.net/pandoc/) then bluemonday should be run after
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these steps. This ensures that no insecure HTML is introduced later in your
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process.
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bluemonday is heavily inspired by both the OWASP Java HTML Sanitizer
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(https://code.google.com/p/owasp-java-html-sanitizer/) and the HTML Purifier
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(http://htmlpurifier.org/).
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We ship two default policies, one is bluemonday.StrictPolicy() and can be
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thought of as equivalent to stripping all HTML elements and their attributes as
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it has nothing on it's whitelist.
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The other is bluemonday.UGCPolicy() and allows a broad selection of HTML
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elements and attributes that are safe for user generated content. Note that
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this policy does not whitelist iframes, object, embed, styles, script, etc.
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The essence of building a policy is to determine which HTML elements and
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attributes are considered safe for your scenario. OWASP provide an XSS
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prevention cheat sheet ( https://www.google.com/search?q=xss+prevention+cheat+sheet )
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to help explain the risks, but essentially:
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1. Avoid whitelisting anything other than plain HTML elements
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2. Avoid whitelisting `script`, `style`, `iframe`, `object`, `embed`, `base`
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elements
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3. Avoid whitelisting anything other than plain HTML elements with simple
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values that you can match to a regexp
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*/
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package bluemonday
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