CVE-2026-84140CWE-346

CVE-2026-84140

Critical · published September 1, 2026

CVSS v3.1
9.8
EPSS
0%
Percentile
7.9
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
9.8 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.00182 · 7.9th percentile
Weakness
CWE-346 · Origin Validation Error
Published
2026-09-01T17:20Z
Affected products (4)
ProductVersionsFixed in
mozilla/firefox< 153.2.0153.2.0
mozilla/firefox≥ 154.0.0, < 155.0.0155.0.0
mozilla/thunderbird< 153.2.0153.2.0
mozilla/thunderbird≥ 154.0, < 155.0155.0
References (5)
https://bugzilla.mozilla.org/show_bug.cgi?id=2063780 · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-82/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-85/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-86/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-88/ · [email protected]
EPSS history
Timeline
  • 03 SEP 03:32Z
    EPSS moved — → 0%
    epss
  • 01 SEP 12:19Z
    Site isolation issue in the DOM: Navigation component
    cvelistv5