github.com/microcosm-cc/bluemonday (go): Package bluemonday provides a way of describing an allowlist of HTML elements and attributes as a policy, and for that policy to be applied to untrusted strings from users that may contain markup. All elements and attributes not on the allowlist will be stripped.  The default bluemonday.UGCPolicy().Sanitize() turns this:  Into the more harmless:  And it turns this:  Into this:  Whilst still allowing this:  To pass through mostly unaltered (it gained a rel="nofollow"):  The primary purpose of bluemonday is to take potentially unsafe user generated content (from things like Markdown, HTML WYSIWYG tools, etc) and make it safe for you to put on your website.  It protects sites against XSS (http://en.wikipedia.org/wiki/Cross-site_scripting) and other malicious content that a user interface may deliver. There are many vectors for an XSS attack (https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet) and the safest thing to do is to sanitize user input against a known safe list of HTML elements and attributes.  Note: You should always run bluemonday after any other processing.  If you use blackfriday (https://github.com/russross/blackfriday) or Pandoc (http://johnmacfarlane.net/pandoc/) then bluemonday should be run after these steps. This ensures that no insecure HTML is introduced later in your process.  bluemonday is heavily inspired by both the OWASP Java HTML Sanitizer (https://code.google.com/p/owasp-java-html-sanitizer/) and the HTML Purifier (http://htmlpurifier.org/).  We ship two default policies, one is bluemonday.StrictPolicy() and can be thought of as equivalent to stripping all HTML elements and their attributes as it has nothing on its allowlist.  The other is bluemonday.UGCPolicy() and allows a broad selection of HTML elements and attributes that are safe for user generated content. Note that this policy does not allow iframes, object, embed, styles, script, etc.  The essence of building a policy is to determine which HTML elements and attributes are considered safe for your scenario. OWASP provide an XSS prevention cheat sheet ( https://www.google.com/search?q=xss+prevention+cheat+sheet ) to help explain the risks, but essentially:
Keywords: allowlist|go|golang|html|owasp|sanitization|security|xss