Package Instance

CKEditor 5 has Cross-site Scripting (XSS) in the HTML Support package
### Impact
A Cross-Site Scripting (XSS) vulnerability has been discovered in the General HTML Support feature. This vulnerability could be triggered by inserting specially crafted markup, leading to unauthorized JavaScript code execution, if the editor instance used an unsafe General HTML Support configuration.

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

* [General HTML Support](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html) is enabled,
* General HTML Support configuration allows inserting unsafe markup (see [Security](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html#security) section to learn more).

### Patches
The problem has been recognized and patched. The fix will be available in version 47.6.0 (and above).

### Workarounds
CKEditor 5 recommends configuring General HTML Support securely to ensure that unsafe content is not accepted. Please refer to the [Security](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html#security) section for detailed guidance.

### Credits
CKEditor 5 would like to thank: 
- Emilio Kevin
- Jeongwoo Lee, Younsoung Kim, Minseok Kim and Jinyeong Kim from ENKI Whitehat

for responsibly reporting this vulnerability.

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

CKEditor5 cross-site scripting vulnerability caused by the editor instance destroying process
### Affected packages
@ckeditor/ckeditor5-markdown-gfm
@ckeditor/ckeditor5-html-support
@ckeditor/ckeditor5-html-embed

### Impact
A cross-site scripting vulnerability has been discovered affecting three optional CKEditor 5's packages. The vulnerability allowed to trigger a JavaScript code after fulfilling special conditions:

a) Using one of the affected packages. In case of `ckeditor5-html-support` and `ckeditor5-html-embed`, additionally, it was required to use a configuration that allows unsafe markup inside the editor,
b) Initializing the editor on an element and using an element other than `<textarea>` as a base,
c) Destroying the editor instance.

The root cause of the issue was a mechanism responsible for updating the source element with the markup coming from the CKEditor 5 data pipeline after destroying the editor. 

This vulnerability might affect a small percent of integrators that depend on dynamic editor initialization/destroy and use [Markdown](https://ckeditor.com/docs/ckeditor5/latest/features/markdown.html), [General HTML Support](https://ckeditor.com/docs/ckeditor5/latest/features/general-html-support.html) or [HTML embed](https://ckeditor.com/docs/ckeditor5/latest/features/html-embed.html) features.

### Patches
The problem has been recognized and patched. The fix will be available in version 35.0.1.

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