Coming Soon and Maintenance Mode < 3.5.3 - Authenticated Stored XSS

Proof of Concept

* Open the Coming Soon plugin's settings (Coming Soon -> Coming Soon) 
* Click on the "Title" section
* Inject XSS payload into the Title section's "Title" form field. 
<!'/*"/*/'/*/"/*--></Script><Image SrcSet=K */; OnError=confirm`123` //>
* Click "Save Section", then reload the settings page (Coming Soon -> Coming Soon)