CVE-2026-84121
CVSS v3
9.6
CRITICAL
EPSS Score
0.3 %
exploit probability, as of 2026-09-28
CISA KEV
No
known exploited
Exploitation
—
SSVC status
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.
Technical details
- Published
- 2026-09-01
- Last Modified
- 2026-09-02
Frequently asked questions
What is CVE-2026-84121?
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.
Is CVE-2026-84121 actively exploited?
Active exploitation of CVE-2026-84121 has not been confirmed. Its EPSS score was 0.3% on 2026-09-28, the estimated probability of exploitation in the next 30 days.
What is the CVSS score for CVE-2026-84121?
CVE-2026-84121 has a CVSS v3 base score of 9.6 (CRITICAL severity).
Is CVE-2026-84121 affecting your environment?
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