by Kastro
Paper/Archive/CVE-2026-84121

CVE-2026-84121

Mozilla Firefox — Sandbox escape due to use-after-free in the DOM: Security component

EPSS 0.3%CVSS 9.6
critical.is priorityof 100
34
CVSS 9.6 (ADP)9.6 / 10 × 3028.8Not in CISA KEV+300.0EPSS percentile 24.9.249 × 205.0No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource
Firefoxsee advisory115.40CNA
Thunderbirdsee advisory140.15CNA

Scores by source

CISA ADP9.6CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
CISA ADPSSVCExploitation: none · Automatable: no · Technical impact: total

References

refbugzilla.mozilla.org/show_bug.cgi?id=2059018refmozilla.org/security/advisories/mfsa2026-82refmozilla.org/security/advisories/mfsa2026-83refmozilla.org/security/advisories/mfsa2026-84refmozilla.org/security/advisories/mfsa2026-85refmozilla.org/security/advisories/mfsa2026-86refmozilla.org/security/advisories/mfsa2026-87refmozilla.org/security/advisories/mfsa2026-88