XSS can occur in GNOME Web (aka Epiphany) before 40.4 and 41.x before 41.1 via an error page.
{ "availability": "No subscription required", "ubuntu_priority": "medium", "binaries": [ { "binary_version": "42.1-1", "binary_name": "epiphany-browser" }, { "binary_version": "42.1-1", "binary_name": "epiphany-browser-data" }, { "binary_version": "42.1-1", "binary_name": "epiphany-browser-dbgsym" } ] }