DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG.
It's also very simple to use and get started with. DOMPurify was [started in February 2014](https://github.com/cure53/DOMPurify/commit/a630922616927373485e0e787ab19e73e3691b2b) and, meanwhile, has reached version 3.0.0.
DOMPurify is written in JavaScript and works in all modern browsers (Safari (10+), Opera (15+), Internet Explorer (10+), Edge, Firefox and Chrome - as well as almost anything else using Blink or WebKit). It doesn't break on MSIE6 or other legacy browsers. It either uses [a fall-back](#what-about-older-browsers-like-msie8) or simply does nothing.
**Note that DOMPurify v2.4.5 is the final version supporting MSIE. For important security updates compatible with MSIE, please use the 2.x branch.**
Our automated tests cover [19 different browsers](https://github.com/cure53/DOMPurify/blob/main/test/karma.custom-launchers.config.js#L5) right now, more to come. We also cover Node.js v14.x, v16.x, v17.x and v18.x, running DOMPurify on [jsdom](https://github.com/jsdom/jsdom). Older Node versions are known to work as well, but hey... no guarantees.
DOMPurify is written by security people who have vast background in web attacks and XSS. Fear not. For more details please also read about our [Security Goals & Threat Model](https://github.com/cure53/DOMPurify/wiki/Security-Goals-&-Threat-Model). Please, read it. Like, really.
## 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 (unless configured otherwise) 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.
Afterwards you can sanitize strings by executing the following code:
```js
let clean = DOMPurify.sanitize(dirty);
```
Or maybe this, if you love working with Angular or alike:
```js
import * as DOMPurify from 'dompurify';
let clean = DOMPurify.sanitize('<b>hello there</b>');
```
The resulting HTML can be written into a DOM element using `innerHTML` or the DOM using `document.write()`. That is fully up to you.
Note that by default, we permit HTML, SVG **and** MathML. If you only need HTML, which might be a very common use-case, you can easily set that up as well:
They can be found here: [@types/dompurify](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/dompurify)
### Is there any foot-gun potential?
Well, please note, if you _first_ sanitize HTML and then modify it _afterwards_, you might easily **void the effects of sanitization**. If you feed the sanitized markup to another library _after_ sanitization, please be certain that the library doesn't mess around with the HTML on its own.
### Okay, makes sense, let's move on
After sanitizing your markup, you can also have a look at the property `DOMPurify.removed` and find out, what elements and attributes were thrown out. Please **do not use** this property for making any security critical decisions. This is just a little helper for curious minds.
### Running DOMPurify on the server
DOMPurify technically also works server-side with Node.js. Our support strives to follow the [Node.js release cycle](https://nodejs.org/en/about/releases/).
Running DOMPurify on the server requires a DOM to be present, which is probably no surprise. Usually, [jsdom](https://github.com/jsdom/jsdom) is the tool of choice and we **strongly recommend** to use the latest version of _jsdom_.
Why? Because older versions of _jsdom_ are known to be buggy in ways that result in XSS _even if_ DOMPurify does everything 100% correctly. There are **known attack vectors** in, e.g. _jsdom v19.0.0_ that are fixed in _jsdom v20.0.0_ - and we really recommend to keep _jsdom_ up to date because of that.
Other than that, you are fine to use DOMPurify on the server. Probably. This really depends on _jsdom_ or whatever DOM you utilize server-side. If you can live with that, this is how you get it to work:
```bash
npm install dompurify
npm install jsdom
```
For _jsdom_ (please use an up-to-date version), this should do the trick:
If you have problems making it work in your specific setup, consider looking at the amazing [isomorphic-dompurify](https://github.com/kkomelin/isomorphic-dompurify) project which solves lots of problems people might run into.
```bash
npm install isomorphic-dompurify
```
```js
import DOMPurify from 'isomorphic-dompurify';
const clean = DOMPurify.sanitize('<s>hello</s>');
```
## Is there a demo?
Of course there is a demo! [Play with DOMPurify](https://cure53.de/purify)
## What if I find a _security_ bug?
First of all, please immediately contact us via [email](mailto:mario@cure53.de) so we can work on a fix. [PGP key](https://keyserver.ubuntu.com/pks/lookup?op=vindex&search=0xC26C858090F70ADA)
Also, you probably qualify for a bug bounty! The fine folks over at [Fastmail](https://www.fastmail.com/) use DOMPurify for their services and added our library to their bug bounty scope. So, if you find a way to bypass or weaken DOMPurify, please also have a look at their website and the [bug bounty info](https://www.fastmail.com/about/bugbounty/).
## Some purification samples please?
How does purified markup look like? Well, [the demo](https://cure53.de/purify) shows it for a big bunch of nasty elements. But let's also show some smaller examples!
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()` API without any known problems.
## What about older browsers like MSIE8?
DOMPurify offers a fall-back behavior for older MSIE browsers. It uses the MSIE-only `toStaticHTML` feature to sanitize. Note however that in this fall-back mode, pretty much none of the configuration flags shown below have any effect. You need to handle that yourself.
If not even `toStaticHTML` is supported, DOMPurify does nothing at all. It simply returns exactly the string that you fed it.
DOMPurify also exposes a property called `isSupported`, which tells you whether DOMPurify will be able to do its job.
## What about DOMPurify and Trusted Types?
In version 1.0.9, support for [Trusted Types API](https://github.com/w3c/webappsec-trusted-types) was added to DOMPurify.
In version 2.0.0, a config flag was added to control DOMPurify's behavior regarding this.
When `DOMPurify.sanitize` is used in an environment where the Trusted Types API is available and `RETURN_TRUSTED_TYPE` is set to `true`, it tries to return a `TrustedHTML` value instead of a string (the behavior for `RETURN_DOM` and `RETURN_DOM_FRAGMENT` config options does not change).
## Can I configure DOMPurify?
Yes. The included default configuration values are pretty good already - but you can of course override them. Check out the [`/demos`](https://github.com/cure53/DOMPurify/tree/main/demos) folder to see a bunch of examples on how you can [customize DOMPurify](https://github.com/cure53/DOMPurify/tree/main/demos#what-is-this).
```js
/**
* General settings
*/
// strip {{ ... }}, ${ ... } and <% ... %> to make output safe for template systems
// be careful please, this mode is not recommended for production usage.
// allowing template parsing in user-controlled HTML is not advised at all.
// only use this mode if there is really no alternative.
var clean = DOMPurify.sanitize(dirty, {SAFE_FOR_TEMPLATES: true});
/**
* Control our allow-lists and block-lists
*/
// allow only <b> elements, very strict
var clean = DOMPurify.sanitize(dirty, {ALLOWED_TAGS: ['b']});
// allow only <b> and <q> with style attributes
var clean = DOMPurify.sanitize(dirty, {ALLOWED_TAGS: ['b', 'q'], ALLOWED_ATTR: ['style']});
// allow all safe HTML elements but neither SVG nor MathML
// note that the USE_PROFILES setting will override the ALLOWED_TAGS setting
// so don't use them together
var clean = DOMPurify.sanitize(dirty, {USE_PROFILES: {html: true}});
// allow all safe SVG elements and SVG Filters, no HTML or MathML
var clean = DOMPurify.sanitize(dirty, {USE_PROFILES: {svg: true, svgFilters: true}});
// allow all safe MathML elements and SVG, but no SVG Filters
var clean = DOMPurify.sanitize(dirty, {USE_PROFILES: {mathMl: true, svg: true}});
// change the default namespace from HTML to something different
var clean = DOMPurify.sanitize(dirty, {NAMESPACE: 'http://www.w3.org/2000/svg'});
// leave all safe HTML as it is and add <style>elementstoblock-list
var clean = DOMPurify.sanitize(dirty, {FORBID_TAGS: ['style']});
// leave all safe HTML as it is and add style attributes to block-list
var clean = DOMPurify.sanitize(dirty, {FORBID_ATTR: ['style']});
// extend the existing array of allowed tags and add <my-tag> to allow-list
var clean = DOMPurify.sanitize(dirty, {ADD_TAGS: ['my-tag']});
// extend the existing array of allowed attributes and add my-attr to allow-list
var clean = DOMPurify.sanitize(dirty, {ADD_ATTR: ['my-attr']});
// prohibit ARIA attributes, leave other safe HTML as is (default is true)
var clean = DOMPurify.sanitize(dirty, {ALLOW_ARIA_ATTR: false});
// prohibit HTML5 data attributes, leave other safe HTML as is (default is true)
var clean = DOMPurify.sanitize(dirty, {ALLOW_DATA_ATTR: false});
/**
* Control behavior relating to Custom Elements
*/
// DOMPurify allows to define rules for Custom Elements. When using the CUSTOM_ELEMENT_HANDLING
// literal, it is possible to define exactly what elements you wish to allow (by default, none are allowed).
//
// The same goes for their attributes. By default, the built-in or configured allow.list is used.
//
// You can use a RegExp literal to specify what is allowed or a predicate, examples for both can be seen below.
// The default values are very restrictive to prevent accidental XSS bypasses. Handle with great care!
var clean = DOMPurify.sanitize(dirty, {IN_PLACE: true}); // see https://github.com/cure53/DOMPurify/issues/288 for more info
```
There is even [more examples here](https://github.com/cure53/DOMPurify/tree/main/demos#what-is-this), showing how you can run, customize and configure DOMPurify to fit your needs.
## Persistent Configuration
Instead of repeatedly passing the same configuration to `DOMPurify.sanitize`, you can use the `DOMPurify.setConfig` method. Your configuration will persist until your next call to `DOMPurify.setConfig`, or until you invoke `DOMPurify.clearConfig` to reset it. Remember that there is only one active configuration, which means once it is set, all extra configuration parameters passed to `DOMPurify.sanitize` are ignored.
## Hooks
DOMPurify allows you to augment its functionality by attaching one or more functions with the `DOMPurify.addHook` method to one of the following hooks:
-`beforeSanitizeElements`
-`uponSanitizeElement` (No 's' - called for every element)
-`afterSanitizeElements`
-`beforeSanitizeAttributes`
-`uponSanitizeAttribute`
-`afterSanitizeAttributes`
-`beforeSanitizeShadowDOM`
-`uponSanitizeShadowNode`
-`afterSanitizeShadowDOM`
It passes the currently processed DOM node, when needed a literal with verified node and attribute data and the DOMPurify configuration to the callback. Check out the [MentalJS hook demo](https://github.com/cure53/DOMPurify/blob/main/demos/hooks-mentaljs-demo.html) to see how the API can be used nicely.
_Example_:
```js
DOMPurify.addHook(
'beforeSanitizeElements',
function (currentNode, hookEvent, config) {
// Do something with the current node and return it
// You can also mutate hookEvent (i.e. set hookEvent.forceKeepAttr = true)
return currentNode;
}
);
```
## Continuous Integration
We are currently using Github Actions in combination with BrowserStack. This gives us the possibility to confirm for each and every commit that all is going according to plan in all supported browsers. Check out the build logs here: https://github.com/cure53/DOMPurify/actions
You can further run local tests by executing `npm test`. The tests work fine with Node.js v0.6.2 and jsdom@8.5.0.
All relevant commits will be signed with the key `0x24BB6BF4` for additional security (since 8th of April 2016).
### Development and contributing
#### Installation (`npm i`)
We support `npm` officially. GitHub Actions workflow is configured to install dependencies using `npm`. When using deprecated version of `npm` we can not fully ensure the versions of installed dependencies which might lead to unanticipated problems.
#### Scripts
We rely on npm run-scripts for integrating with our tooling infrastructure. We use ESLint as a pre-commit hook to ensure code consistency. Moreover, to ease formatting we use [prettier](https://github.com/prettier/prettier) while building the `/dist` assets happens through `rollup`.
These are our npm scripts:
-`npm run dev` to start building while watching sources for changes
-`npm run test` to run our test suite via jsdom and karma
-`test:jsdom` to only run tests through jsdom
-`test:karma` to only run tests through karma
-`npm run lint` to lint the sources using ESLint (via xo)
-`npm run format` to format our sources using prettier to ease to pass ESLint
-`npm run build` to build our distribution assets minified and unminified as a UMD module
-`npm run build:umd` to only build an unminified UMD module
-`npm run build:umd:min` to only build a minified UMD module
Note: all run scripts triggered via `npm run <script>`.
There are more npm scripts but they are mainly to integrate with CI or are meant to be "private" for instance to amend build distribution files with every commit.
## Security Mailing List
We maintain a mailing list that notifies whenever a security-critical release of DOMPurify was published. This means, if someone found a bypass and we fixed it with a release (which always happens when a bypass was found) a mail will go out to that list. This usually happens within minutes or few hours after learning about a bypass. The list can be subscribed to here:
And last but not least, thanks to [BrowserStack Open-Source Program](https://www.browserstack.com/open-source) for supporting this project with their services for free and delivering excellent, dedicated and very professional support on top of that.
