FooGallery < 2.0.35 - Authenticated Stored Cross-Site Scripting

Description

In the plugin, the Custom CSS field of each gallery is not properly sanitised or validated before being being output in the page where the gallery is embed, leading to a stored Cross-Site Scripting issue.

Proof of Concept

Create or edit a gallery and add the following payload in the Custom CSS field: </style><svg/onload=alert(document.domain)>
Then, view the embed gallery (which must have at least one image) in a page or post to trigger the XSS