CVE-2026-16387

Site isolation issue in the Networking component

Critical · published July 21, 2026

CVSS v3.1
9.8
EPSS
0%
Percentile
9.9
In the wild
Unconfirmed
What it is

Site isolation issue in the Networking component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

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
0.00204 · 9.9th percentile
Published
2026-07-21T12:38Z
EPSS history
Timeline
  • 21 JUL 12:38Z
    Site isolation issue in the Networking component
    cvelistv5