Vulnerability Instance

Cross-site scripting (XSS) in the clipboard package
### Impact
During a recent internal audit, we identified a Cross-Site Scripting (XSS) vulnerability in the CKEditor 5 clipboard package. This vulnerability could be triggered by a specific user action, leading to unauthorized JavaScript code execution, if the attacker managed to insert a malicious content into the editor, which might happen with a very specific editor configuration.

This vulnerability affects **only** installations where the editor configuration meets the following criteria:

1. The [**Block Toolbar**](https://ckeditor.com/docs/ckeditor5/latest/getting-started/setup/toolbar.html#block-toolbar) plugin is enabled.
1. One of the following plugins is also enabled:
    - [**General HTML Support**](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html) with a configuration that permits unsafe markup.
    - [**HTML Embed**](https://ckeditor.com/docs/ckeditor5/latest/features/html/html-embed.html).

### Patches
The problem has been recognized and patched. The fix will be available in version 43.1.1 (and above), and explicitly in version 41.3.2.

### Workarounds
It's highly recommended to update to the version 43.1.1 or higher. However, if the update is not an option, we recommend disabling the block toolbar plugin.

### For more information
Email us at [security@cksource.com](mailto:security@cksource.com) if you have any questions or comments about this advisory.