CVE-2021-4140

10.0 criticalEPSS 1.4%

Critical (10.0) in mozilla. EPSS 1.4% chance of exploitation in the next 30 days.

It was possible to construct specific XSLT markup that would be able to bypass an iframe sandbox. This vulnerability affects Firefox ESR < 91.5, Firefox < 96, and Thunderbird < 91.5.

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: 1.4% chance of exploitation in the next 30 days; higher than 72% of CVEs (scores of 2026-10-31)
CWE: CWE-91
Published: 2022-12-22
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

mozilla:firefox
mozilla:firefox_esr
mozilla:thunderbird

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1746720
https://www.mozilla.org/security/advisories/mfsa2022-01/
https://www.mozilla.org/security/advisories/mfsa2022-02/
https://www.mozilla.org/security/advisories/mfsa2022-03/
https://bugzilla.mozilla.org/show_bug.cgi?id=1746720

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