CVE-2021-38503
The iframe sandbox rules were not correctly applied to XSLT stylesheets, allowing an iframe to bypass restrictions such as executing scripts or navigating the top-level frame. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3. Date published : 2021-12-08 https://bugzilla.mozilla.org/show_bug.cgi?id=1729517