Critical 9.6Published Sep 1, 2026

CVE-2026-84121Sandbox escape due to use-after-free in the DOM: Security component

Updated under an hour ago (Oct 26, 2026, 4:23 PM ET)

Does this affect you?

It affects Mozilla Firefox and 1 other product. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

Do this next

Start free and add your stack

Free account, 1 product

Every CVE for Mozilla Firefox

Exploited in the last 30 days

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.

CVSS: 9.6 CRITICAL (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Weakness (CWE): CWE-416
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: mozilla
NVD analysis: Analyzed
Record last updated: Sep 1, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Mozilla Firefox mozilla:firefox (from the name)	115.40 builds before 115.* not affected; 140.15 builds before 140.* not affected; 153.2 builds before 153.* not affected; from 155 not affected	CNA record
Mozilla Thunderbird mozilla:thunderbird (from the name)	140.15 builds before 140.* not affected; 153.2 builds before 153.* not affected; from 155 not affected	CNA record
mozilla firefox mozilla:firefox	before 115.40.0; from 116.0 before 140.15.0; from 141.0.0 before 153.2.0; from 154.0.0 before 155.0.0	NVD
mozilla thunderbird mozilla:thunderbird	before 140.15.0; from 141.0 before 153.2.0; from 154.0 before 155.0	NVD

References

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2059018	permissions-required
https://www.mozilla.org/security/advisories/mfsa2026-82/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-83/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-84/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-85/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-86/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-87/	vendor-advisory
https://www.mozilla.org/security/advisories/mfsa2026-88/	vendor-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.