CVE-2026-74986CWE-200information-disclosure

CVE-2026-74986

Critical · published August 18, 2026

CVSS v3.1

9.1

EPSS

Percentile

45.5

In the wild

Unconfirmed

What it is

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.

The record

Technical detail

CVSS v3.1: 9.1 · CRITICAL
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CVSS v4.0: Not supplied
EPSS: 0.00555 · 45.5th percentile
Weakness: CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor
Published: 2026-08-18T17:17Z

Affected products (2)

Product	Versions	Fixed in
mozilla/firefox	< 153.1.0	153.1.0
mozilla/thunderbird	< 153.1.0	153.1.0

References (5)

https://bugzilla.mozilla.org/show_bug.cgi?id=2060048 · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-74/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-77/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-78/ · [email protected]https://www.mozilla.org/security/advisories/mfsa2026-80/ · [email protected]

EPSS history

Timeline

18 AUG 12:23Z
Site isolation issue in the CSS Parsing and Computation component
cvelistv5