CVE-2026-84121

critical

Description

Sandbox escape due to use-after-free in the DOM: Security component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

References

https://www.mozilla.org/security/advisories/mfsa2026-88/

https://www.mozilla.org/security/advisories/mfsa2026-87/

https://www.mozilla.org/security/advisories/mfsa2026-86/

https://www.mozilla.org/security/advisories/mfsa2026-85/

https://www.mozilla.org/security/advisories/mfsa2026-84/

https://www.mozilla.org/security/advisories/mfsa2026-83/

https://www.mozilla.org/security/advisories/mfsa2026-82/

https://bugzilla.mozilla.org/show_bug.cgi?id=2059018

Details

Source: Mitre, NVD

Published: 2026-09-01

Updated: 2026-09-01

Risk Information

CVSS v2

Base Score: 10

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

Severity: Critical

CVSS v3

Base Score: 9.6

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