CVE-2021-38503: Mozilla: iframe sandbox rules did not apply to XSLT stylesheets

Severity: Critical

CVSS Score: 10

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.