GHSA-vv3r-fxqp-vr3f: XSS via uploaded gpx file

A malicious content author could upload a GPX file with a Javascript payload. The payload could then be executed by luring a legitimate user to view the file in a browser with support for GPX files. GPX is an XML-based format used to store GPS data.

By default, Silverstripe CMS will no longer allow GPX files to be uploaded to the assets area.