CVE-2026-84121
Last modified
CVE-2026-84121 is a critical-severity vulnerability rated 9.6/10 on the CVSS scale. 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.. EPSS estimates a 0.34% chance of exploitation in the next 30 days.
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.
Metrics
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | < 115.40.0 |
| Mozilla | Firefox | >= 116.0, < 140.15.0 |
| Mozilla | Firefox | >= 141.0.0, < 153.2.0 |
| Mozilla | Firefox | >= 154.0.0, < 155.0.0 |
| Mozilla | Thunderbird | < 140.15.0 |
| Mozilla | Thunderbird | >= 141.0, < 153.2.0 |
| Mozilla | Thunderbird | >= 154.0, < 155.0 |
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2059018Permissions 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
Timeline
- Published
- Last Modified
- Status
- Analyzed
Frequently Asked Questions
What is CVE-2026-84121?
How severe is CVE-2026-84121?
How do I fix CVE-2026-84121?
How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
Related CVEs from 2026
- CVE-2026-84115A vulnerability was found in Cleo Harmony up to 5.8.1.10. Th…8.3
- CVE-2026-84117Privilege escalation in Firefox for Android. This vulnerabil…8.8
- CVE-2026-84118Use-after-free in the JavaScript: GC component. This vulnera…5.4
- CVE-2026-84119Sandbox escape due to use-after-free in the DOM: Navigation …9.6
- CVE-2026-8412Concrete CMS 9 before 9.5.0 is vulnerable to Cross Site Requ…8.8
- CVE-2026-84120Use-after-free in the Audio/Video component. This vulnerabil…5.4
- CVE-2026-84122Use-after-free in the Audio/Video component. This vulnerabil…5.4
- CVE-2026-84123Privilege escalation due to use-after-free in the Graphics: …8.8
- CVE-2026-84124Use-after-free in the DOM: Core & HTML component. This vulne…5.4
- CVE-2026-84125Use-after-free in the DOM: Core & HTML component. This vulne…5.4
- CVE-2026-84126Incorrect boundary conditions in the Layout: Grid component.…4.3
- CVE-2026-84127Information disclosure in the WebExtensions component in Fir…4.3
Are you affected by CVE-2026-84121?
Run a free Strix scan to check your systems for this vulnerability.
Scan your code nowSource: NVD / NIST