CVE-2021-38503

10.0 criticalEPSS 4.1%

Critical (10.0). EPSS 4.1% chance of exploitation in the next 30 days.

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.

Severity

CVSS 3.1

10.0 critical

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS: 4.1% chance of exploitation in the next 30 days; higher than 90% of CVEs (scores of 2026-10-31)
CWE: CWE-863
Published: 2021-12-08
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

debian:debian_linux
mozilla:firefox
mozilla:firefox_esr
mozilla:thunderbird

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

Check your stack JSON