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html-embed.md 7.3 KB


category: features

menu-title: HTML embed

HTML embed

The {@link module:html-embed/htmlembed~HtmlEmbed} plugin allows embedding an arbitrary HTML snippet in the editor. The feature is targeted at more advanced users who want to directly interact with HTML fragments.

This feature can be used to embed any HTML code and bypass CKEditor 5's filtering mechanisms. Thanks to that it is possible to enrich content produced by CKEditor 5 with fragments of HTML that are not supported by any other CKEditor 5 feature.

Example of content that can be embedded thanks to the HTML embed feature:

  • analytics code (that usually require embedding <script> elements),
  • social page widgets (that also require embedding <script> elements),
  • content embeddable by <iframe>s,
  • HTML media elements such as audio and video,
  • HTML snippets produced by external tools (e.g reports),
  • interactive content that requires a combination of rich HTML and scripts.

It is recommended to use the {@link features/media-embed media embed} feature for embeddable media that are supported by this feature. The HTML embed feature can be used to handle remaining content.

Read the [Security](#security) section before installing this plugin.

Incorrect configuration may **lead to security issues**.

Demo

Use the editor below to see the plugin in action. Click the "Preview editor data" button below the editor to see a preview of the editor content, including embedded HTML.

{@snippet features/html-embed}

Installation

To add this feature to your rich-text editor, install the @ckeditor/ckeditor5-html-embed package:

npm install --save @ckeditor/ckeditor5-html-embed

And add it to your plugin list configuration:

import HtmlEmbed from '@ckeditor/ckeditor5-html-embed/src/htmlembed';

ClassicEditor
	.create( document.querySelector( '#editor' ), {
		plugins: [ HtmlEmbed, ... ],
		toolbar: [ 'htmlEmbed', ... ],
	} )
	.then( ... )
	.catch( ... );

Read more about {@link builds/guides/integration/installing-plugins installing plugins}.

Configuration

Content previews

The feature is by default configured to not show previews of the HTML snippets. The previews can be enabled by setting the {@link module:html-embed/htmlembed~HtmlEmbedConfig#showPreviews config.htmlEmbed.showPreviews} option to true.

However, by showing previews of embedded HTML snippets you expose the users of your system to the risk of executing malicious JavaScript code inside the editor. Therefore, it is highly recommended to plug an HTML sanitizier that will strip the malicious code from create snippets before rendering their previous. The sanitizer can be plugged by defining the {@link module:html-embed/htmlembed~HtmlEmbedConfig#sanitizeHtml config.htmlEmbed.sanitizeHtml} option.

ClassicEditor
	.create( document.querySelector( '#editor' ), {
		plugins: [ HtmlEmbed, ... ],
		toolbar: [ 'htmlEmbed', ... ],
		htmlEmbed: {
			showPreviews: true,
			sanitizeHtml: ( inputHtml ) => {
				// Strip unsafe elements and attributes, e.g.:
				// the `<script>` elements and `on*` attributes.
				const outputHtml = sanitize( inputHtml );

				return {
					html: outputHtml,
					// true or false depending on whether the sanitizer stripped anything.
					hasChanged: true
				};
			}
		}
	} )
	.then( ... )
	.catch( ... );

Currently, the feature does not execute <script> tags so content that requires executing JavaScript in order to generate a preview will not show in the editor. However, other JavaScript code – e.g. used in on* observers and scr="javascript:..." attributes will be executed and therefore a sanitizer still needs to be enabled.

Read more about the security aspect in the next section.

Security

If the HTML embed feature is configured to show content previews, the HTML that the user inserts into the HTML embed widget is then rendered back to the user. If the HTML was rendered as-is, any JavaScript code included in these HTML snippets would be executed by the browser in context of your website.

This, in turn, is a plain security risk. The HTML provided by the user might be mistakenly copied from a malicious website or end up in the users clipboard (as it would usually be copied and pasted) by any other mean.

In some cases, advanced users can be instructed to never paste HTML code from untrusted sources. However, in most cases, it is highly recommended to properly secure the system by configuring the HTML embed feature to use an HTML sanitizer and, optionally, setting strict CSP rules.

The HTML embed feature [does not currently execute code in `<script>` tags](https://github.com/ckeditor/ckeditor5/issues/8326). However, it will execute code in `on*` and `scr="javascript:..."` attributes.

The tricky part is that some HTML snippets require JavaScript to be executed to render any meaningful previews (e.g. Facebook embeds). Some, in turn, does not make sense to be executed (analytics code).

Therefore, when configuring the sanitizer and CSP rules, you can take those situations into consideration and for instance allow `<script>` tags pointing only to certain domains (e.g. a trusted external page that requires JavaScript).

Sanitizer

The {@link module:html-embed/htmlembed~HtmlEmbedConfig#sanitizeHtml config.htmlEmbed.sanitizeHtml} option allow plugging an external sanitizer.

Some popular JavaScript libraries that can be used include sanitize-html and DOMPurify.

The default settings of these libraries usually strip all potentially malicious content including <iframe>, <video>, etc. elements and JavaScript code coming from trusted sources so you may need to adjust their settings to match your needs.

CSP

In addition to using a sanitizer you can use the built browser mechanism called Content Security Policy. By using CSP you can let the browser know what sources and means to execute JavaScript code and include other resources such as stylesheets, images and fonts are allowed.

Common API

The {@link module:html-embed/htmlembed~HtmlEmbed} plugin registers:

  • the UI button component ('htmlEmbed'),
  • the 'updateHtmlEmbed' command implemented by {@link module:html-embed/updatehtmlembedcommand~UpdateHtmlEmbedCommand}.
  • the 'insertHtmlEmbed' command implemented by {@link module:html-embed/inserthtmlembedcommand~InsertHtmlEmbedCommand}.

Both commands can be executed using the {@link module:core/editor/editor~Editor#execute editor.execute()} method:

editor.execute( 'insertHtmlEmbed' );
editor.execute( 'updateHtmlEmbed', '<p>HTML string</p>' );

We recommend using the official {@link framework/guides/development-tools#ckeditor-5-inspector CKEditor 5 inspector} for development and debugging. It will give you tons of useful information about the state of the editor such as internal data structures, selection, commands, and many more.

Contribute

The source code of the feature is available on GitHub in https://github.com/ckeditor/ckeditor5/tree/master/packages/ckeditor5-html-embed.