CVE-2026-74986

CriticalCVSS 9.1/10Last modified Aug 25, 2026

Description

Site isolation issue in the CSS Parsing and Computation component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

Metrics

CVSS 3.1 9.1/10CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Weakness enumeration

CWE-200

Affected software

Vendor	Product	Versions
Mozilla	Firefox	—
Mozilla	Thunderbird	—

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2060048Permissions Required
https://www.mozilla.org/security/advisories/mfsa2026-74/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-77/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-78/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-80/Vendor Advisory

Timeline

Published: Aug 18, 2026
Last modified: Aug 25, 2026
NVD status: Analyzed

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