{"cve":"CVE-2021-38503","nvd":{"published":"2021-12-08T22:15:08.737","modified":"2026-06-17T04:02:14.397","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","score":10.0},"cwes":["CWE-863"],"references":["https://bugzilla.mozilla.org/show_bug.cgi?id=1729517","https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html","https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html","https://security.gentoo.org/glsa/202202-03","https://security.gentoo.org/glsa/202208-14"],"products":["debian:debian_linux","mozilla:firefox","mozilla:firefox_esr","mozilla:thunderbird"],"source":"nvd","synced_at":"2026-10-19T21:25:41.256909649+00:00"},"epss":{"cve":"CVE-2021-38503","score":0.04116,"percentile":0.90784,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}