CVE-2026-100778
CRITICALCVSS 9.6/10EPSS 0.34%
Last modified
CVE-2026-100778 is a critical-severity vulnerability rated 9.6/10 on the CVSS scale. Sandbox escape due to use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.. EPSS estimates a 0.34% chance of exploitation in the next 30 days.
Description
Sandbox escape due to use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
Metrics
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | >= 115.0.1, < 115.42.0 |
| Mozilla | Firefox | >= 140.0.0, < 140.17.0 |
| Mozilla | Firefox | >= 153.0, < 153.4.0 |
| Mozilla | Firefox | >= 154.0.0, < 157.0.0 |
| Mozilla | Thunderbird | >= 140.0, < 140.17.0 |
| Mozilla | Thunderbird | >= 153.0, < 153.4.0 |
| Mozilla | Thunderbird | >= 154.0, < 157.0 |
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2068406Permissions Required
- https://www.mozilla.org/security/advisories/mfsa2026-100/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-101/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-102/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-103/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-97/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-98/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-99/Vendor Advisory
Timeline
- Published
- Last Modified
- Status
- Analyzed
Frequently Asked Questions
What is CVE-2026-100778?
Sandbox escape due to use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
How severe is CVE-2026-100778?
CVE-2026-100778 has a CVSS score of 9.6/10 (CRITICAL severity). The EPSS model estimates a 0.34% probability of exploitation in the next 30 days.
How do I fix CVE-2026-100778?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.
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.
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