What is dompurify?
DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML, and SVG. It helps prevent Cross-Site Scripting (XSS) attacks by sanitizing HTML content to ensure it's safe to insert into the DOM. It is written in JavaScript and works in all modern web browsers.
What are dompurify's main functionalities?
Sanitizing HTML strings
This feature allows you to sanitize HTML strings to prevent XSS attacks. The code sample demonstrates how to sanitize a string that contains a potentially malicious script. The result of this code would be a safe string with the malicious parts removed.
DOMPurify.sanitize('<img src=x onerror=alert(1)//>');
Configuring the sanitizer
DOMPurify can be configured to allow certain tags, attributes, or schemes. In the code sample, the sanitizer is configured to allow only 'img' tags and will strip out any other tags, including scripts or event handlers.
DOMPurify.sanitize('<img src=x onerror=alert(1)//>', {ALLOWED_TAGS: ['img']});
Hooking into sanitization
DOMPurify allows you to add hooks that can modify the content during the sanitization process. In the code sample, a hook is added that will be called after the attributes of all nodes have been sanitized, allowing for custom manipulation of the nodes.
DOMPurify.addHook('afterSanitizeAttributes', function(node) { /* manipulate node */ });
Other packages similar to dompurify
sanitize-html
sanitize-html is another HTML sanitizer that can clean up user-generated HTML, preventing XSS attacks. It is similar to DOMPurify but has a different API and set of defaults. It also allows for a high degree of customization in terms of what tags and attributes are allowed.
xss
xss is a package that aims to filter input from users to prevent XSS attacks. It is similar to DOMPurify but includes different options and is more focused on filtering input as opposed to sanitizing existing HTML content.
DOMPurify
DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG. It's written in JavaScript and works in all modern browsers (Safari, Opera (15+), Internet Explorer (9+), Firefox and Chrome - as well as almost anything else using Blink or WebKit). DOMPurify is written by security people who have vast background in web attacks and XSS. Fear not.
What does it do?
DOMPurify sanitizes HTML and prevents XSS attacks. You can feed DOMPurify with string full of dirty HTML and it will return a string with clean HTML. DOMPurify will strip out everything that contains dangerous HTML and thereby prevent XSS attacks and other nastiness. It's also damn bloody fast. We use the technologies the browser provides and turn them into an XSS filter. The faster your browser, the faster DOMPurify will be.
How do I use it?
It's easy. Just include DOMPurify on your website.
<script type="text/javascript" src="purify.js"></script>
Afterwards you can sanitize strings by executing the following code:
var clean = DOMPurify.sanitize(dirty);
If you're using an AMD module loader like Require.js, you can load this script asynchronously as well:
require(['dompurify'], function(DOMPurify) {
var clean = DOMPurify.sanitize(dirty);
};
Is there a demo?
Of course there is a demo! Play with DOMPurify
Some samples please?
How does purified markup look like? Well, the demo shows it for a big bunch of nasty elements. But let's also show some smaller examples!
DOMPurify.sanitize('<img src=x onerror=alert(1)//>');
DOMPurify.sanitize('<svg><g/onload=alert(2)//<p>');
DOMPurify.sanitize('<p>abc<iframe/\/src=jAva	script:alert(3)>def');
DOMPurify.sanitize('<math><mi//xlink:href="data:x,<script>alert(4)</script>">');
DOMPurify.sanitize('<TABLE><tr><td>HELLO</tr></TABL>');
DOMPurify.sanitize('<UL><li><A HREF=//google.com>click</UL>');
What is supported?
DOMPurify currently supports HTML5, SVG and MathML. DOMPurify per default allows CSS, HTML custom data attributes. DOMPurify also supports the Shadow DOM - and sanitizes DOM templates recursively. DOMPurify also allows you to sanitize HTML for being used with the jQuery $()
and elm.html()
methods.
Can I configure it?
Yes. The included default configuration values are pretty good already - but you can of course override them:
var clean = DOMPurify.sanitize(dirty, {ALLOWED_TAGS: ['b']});
var clean = DOMPurify.sanitize(dirty, {ALLOWED_TAGS: ['b', 'q'], ALLOWED_ATTR: ['style']});
var clean = DOMPurify.sanitize(dirty, {ADD_TAGS: ['my-tag']});
var clean = DOMPurify.sanitize(dirty, {ADD_ATTR: ['my-attr']});
var clean = DOMPurify.sanitize(dirty, {ALLOW_DATA_ATTR: false});
var clean = DOMPurify.sanitize(dirty, {RETURN_DOM: true});
var clean = DOMPurify.sanitize(dirty, {WHOLE_DOCUMENT: true});
var clean = DOMPurify.sanitize(dirty, {SAFE_FOR_JQUERY: true});
var clean = DOMPurify.sanitize(dirty, {SANITIZE_DOM: false});
var clean = DOMPurify.sanitize(dirty, {KEEP_CONTENT: false});
Unit tests
To run the test suite, you need Node.js first. Install the dependencies with npm install
, then start the test server with npm test
. You can run the tests in your browser from http://localhost:8000/test/.
What's on the road-map?
Still a lot of things although we have come far feature-wise. We're currently considering to build a CSS module, that cleans up inside <style>
elements - and not only style
attributes. Future versions will also, most likely, reliably prevent leakage via HTTP requests, proxy HTTP requests etc. etc.
Who contributed?
Several people need to be listed here! @garethheyes for invaluable help, @shafigullin for breaking the library multiple times and thereby strengthening it, @mmrupp and @irsdl for doing the same. Big thanks also go to @mathias, @cgvwzq, @robbertatwork, @giutro and @fhemberger!