github.com/insionng/yougam@v0.0.0-20170714101924-2bc18d833463/libraries/bluemonday/doc.go (about)

     1  // Copyright (c) 2014, David Kitchen <david@buro9.com>
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    29  
    30  /*
    31  Package bluemonday provides a way of describing a whitelist of HTML elements
    32  and attributes as a policy, and for that policy to be applied to untrusted
    33  strings from users that may contain markup. All elements and attributes not on
    34  the whitelist will be stripped.
    35  
    36  The default bluemonday.UGCPolicy().Sanitize() turns this:
    37  
    38      Hello <STYLE>.XSS{background-image:url("javascript:alert('XSS')");}</STYLE><A CLASS=XSS></A>World
    39  
    40  Into the more harmless:
    41  
    42      Hello World
    43  
    44  And it turns this:
    45  
    46      <a href="javascript:alert('XSS1')" onmouseover="alert('XSS2')">XSS<a>
    47  
    48  Into this:
    49  
    50      XSS
    51  
    52  Whilst still allowing this:
    53  
    54      <a href="http://www.google.com/">
    55        <img src="https://ssl.gstatic.com/accounts/ui/logo_2x.png"/>
    56      </a>
    57  
    58  To pass through mostly unaltered (it gained a rel="nofollow"):
    59  
    60      <a href="http://www.google.com/" rel="nofollow">
    61        <img src="https://ssl.gstatic.com/accounts/ui/logo_2x.png"/>
    62      </a>
    63  
    64  The primary purpose of bluemonday is to take potentially unsafe user generated
    65  content (from things like Markdown, HTML WYSIWYG tools, etc) and make it safe
    66  for you to put on your website.
    67  
    68  It protects sites against XSS (http://en.wikipedia.org/wiki/Cross-site_scripting)
    69  and other malicious content that a user interface may deliver. There are many
    70  vectors for an XSS attack (https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet)
    71  and the safest thing to do is to sanitize user input against a known safe list
    72  of HTML elements and attributes.
    73  
    74  Note: You should always run bluemonday after any other processing.
    75  
    76  If you use blackfriday (https://yougam/libraries/russross/blackfriday) or
    77  Pandoc (http://johnmacfarlane.net/pandoc/) then bluemonday should be run after
    78  these steps. This ensures that no insecure HTML is introduced later in your
    79  process.
    80  
    81  bluemonday is heavily inspired by both the OWASP Java HTML Sanitizer
    82  (https://code.google.com/p/owasp-java-html-sanitizer/) and the HTML Purifier
    83  (http://htmlpurifier.org/).
    84  
    85  We ship two default policies, one is bluemonday.StrictPolicy() and can be
    86  thought of as equivalent to stripping all HTML elements and their attributes as
    87  it has nothing on it's whitelist.
    88  
    89  The other is bluemonday.UGCPolicy() and allows a broad selection of HTML
    90  elements and attributes that are safe for user generated content. Note that
    91  this policy does not whitelist iframes, object, embed, styles, script, etc.
    92  
    93  The essence of building a policy is to determine which HTML elements and
    94  attributes are considered safe for your scenario. OWASP provide an XSS
    95  prevention cheat sheet ( https://www.google.com/search?q=xss+prevention+cheat+sheet )
    96  to help explain the risks, but essentially:
    97  
    98      1. Avoid whitelisting anything other than plain HTML elements
    99      2. Avoid whitelisting `script`, `style`, `iframe`, `object`, `embed`, `base`
   100         elements
   101      3. Avoid whitelisting anything other than plain HTML elements with simple
   102         values that you can match to a regexp
   103  */
   104  package bluemonday