Browser crash in Safari 10.0.1 when CKEditor is given a particular template

[Nick Willett-Jeffries]

Steps to reproduce

1. In Safari 10.0.1, navigate to this CKEditor demo page: ​http://sdk.ckeditor.com/samples/classic.html
2. Switch to "Source" mode on the "Classic Editor with Default Styles"
3. Copy the html in the file attached to this ticket into the editor.
4. Switch back to "WYSIWYG" mode by clicking "Source" again.
5. Click on the document in the editor. Browser tab should hang. If you open a task manager you should observe the Safari process consuming 100% CPU.

Other details (browser, OS, CKEditor version, installed plugins)

• Only occurs in Safari 10.0.1 to my knowledge.
• You'll notice that the attached html includes conditional tags recognized by Microsoft Outlook (if (get mso 9) etc...). These are common in html emails for compatibility purposes with Outlook. Remove them and Safari no longer crashes in this manner.

[kkrzton]

I can confirm it happens only on Safari 10.1. Tested with CKEditor 4.6.1.