CVE-2026-84140
CRITICALCVSS 9.8/10EPSS 0.14%
Last modified
CVE-2026-84140 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.. EPSS estimates a 0.14% chance of exploitation in the next 30 days.
Description
Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
Metrics
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | < 153.2.0 |
| Mozilla | Firefox | >= 154.0.0, < 155.0.0 |
| Mozilla | Thunderbird | < 153.2.0 |
| Mozilla | Thunderbird | >= 154.0, < 155.0 |
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2063780Issue Tracking, Permissions Required
- https://www.mozilla.org/security/advisories/mfsa2026-82/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/mfsa2026-88/Vendor Advisory
Timeline
- Published
- Last Modified
- Status
- Modified
Frequently Asked Questions
What is CVE-2026-84140?
Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
How severe is CVE-2026-84140?
CVE-2026-84140 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.14% probability of exploitation in the next 30 days.
How do I fix CVE-2026-84140?
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.
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Are you affected by CVE-2026-84140?
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Scan your code nowSource: NVD / NIST