CVE-2021-4140

Mozilla: Iframe sandbox bypass with XSLT

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Severity

Important

Red Hat Product Security

9.6

CVSS 3.1

Review impact separately from score.

Published · January 11, 2022

Updated · November 21, 2025

Description

The Mozilla Foundation Security Advisory describes this flaw as:

It was possible to construct specific XSLT markups that would enable someone to bypass an iframe sandbox.

Statement

Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.

CVSS score applicability

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation

No mitigation is specified in collected source.

CVSS / CWE

CVSS 3.1 · 9.6
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

CWE-1021 · Improper Restriction of Rendered UI Layers or Frames