CVE-2021-43831: Files on the host computer can be accessed from the Gradio interface

This is a vulnerability that affects anyone who creates and publicly shares Gradio interfaces using gradio<2.4.8. Because of the way that static files were being served, someone who generated a public Gradio link and shared it with others would potentially be exposing the files on the computer that generated the link, while the link was active. An attacker would be able to view the contents of a file on the computer if they knew the exact relative filepath. We do not have any evidence that this was ever exploited, but we treated the issue seriously and immediately took steps to mitigate it (see below)