A XSS vulnerability exists in the getTip() method of Action Columns.

The Ext JS framework brings no built-in XSS protection, meaning that
developers are responsible for sanitizing their output. However. the method
above takes HTML-escaped data and un-escapes it. Therefore if the tooltip
contains user-controlled data a XSS is possible.

A fiddle demonstrating the issue can be found here:
https://fiddle.sencha.com/#fiddle/2e3k&view/editor

The vendor tracked this issue with the internal ID  EXTJS-26864.

MITRE assigned  CVE-2018-8046 to this issue.

This issue has been fixed in version 6.6.0, the release notes are available
here: http://examples.sencha.com/extjs/6.6.0/release-notes.html

Best Regards,
Daniel