CVE-2026-74986

CRITICAL 9.1CVE-2026-74986 · Published 18/08/2026 · updated 25/08/2026

Package	Affected versions	Patched versions
firefox mozilla	`< 153.1.0`	`153.1.0`
thunderbird mozilla	`< 153.1.0`	`153.1.0`

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.

References

bugzilla.mozilla.org/show_bug.cgi · Permissions Required
mozilla.org/security/advisories/mfsa2026-74 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-77 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-78 · Vendor Advisory
mozilla.org/security/advisories/mfsa2026-80 · Vendor Advisory

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