5.7.6 contains a security fix for a cross-site inclusion (XSSI)
vulnerability, where files at a known URL could be included in a page
from an unauthorized website if the user is logged into a Jupyter
server. The fix involves setting the X-Content-Type-Options: nosniff
header, and applying CSRF checks previously on all non-GET API requests
to GET requests to API endpoints and the /files/ endpoint.
The attacking page is able to access some contents of files when using
Internet Explorer through script errors, but this has not been
demonstrated with other browsers. A CVE has been requested for this
vulnerability.