XSS can occur in GNOME Web (aka Epiphany) before 40.4 and 41.x before 41.1 via an about: page, as demonstrated by ephy-about:overview when a user visits an XSS payload page often enough to place that page on the Most Visited list. CREATE(Triage):(User=admin) CVE-2021-45085 (https://nvd.nist.gov/vuln/detail/CVE-2021-45085)
