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Fencer Vulns
critical 9.1

CVE-2026-74986 json

Site isolation issue in the CSS Parsing and Computation component

published 2026-08-18 2 mo ago modified 2026-08-25 2 mo ago also EUVD-2026-60698

cvss
9.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 46%
public exploits
0
none known

Summary

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.

Patch / fix

  • mozilla firefox 153.1
  • mozilla firefox_esr 153.1
  • mozilla thunderbird 153.1
  • mozilla thunderbird_esr 153.1
  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 153.2.0-150400.13.3.1
  • mozilla-nss SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +11 more 3.125-150400.3.74.1
  • mozilla-nspr SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +11 more 4.39-150400.12.3.1
  • MozillaFirefox SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 153.2.0-150400.157.5.1
  • MozillaFirefox-branding-SLE SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 153-150400.14.3.1
  • mozilla-nss SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 3.125-160000.1.1
  • mozilla-nspr SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 4.39-160000.1.1
  • rust-cbindgen SLES for SAP applications 16.0, SLES 16.0 0.29.4+git0-160000.1.1

suse advisories SUSE-SU-2026:4268-1SUSE-SU-2026:4156-1SUSE-SU-2026:4140-1SUSE-SU-2026:23411-1SUSE-SU-2026:23590-1SUSE-SU-2026:3683-1

  • MozillaThunderbird openSUSE Tumbleweed 153.4.0-1.1
  • rust-cbindgen openSUSE Leap 16.0 0.29.4+git0-160000.1.1
  • mozilla-nss openSUSE Leap 16.0 3.125-160000.1.1
  • mozilla-nspr openSUSE Leap 16.0 4.39-160000.1.1
  • MozillaFirefox openSUSE Leap 16.0 153.1.0-160000.1.2
  • MozillaFirefox openSUSE Tumbleweed 154.0-1.1
  • firefox-esr openSUSE Tumbleweed 153.1.0-1.1

opensuse advisories openSUSE-SU-2026:12098-1openSUSE-SU-2026:21713-1openSUSE-SU-2026:11580-1openSUSE-SU-2026:11546-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-74986 updated cvss 3.4

firefox: thunderbird: Site isolation issue in the CSS Parsing and Computation component

  • Red Hat Enterprise Linux 6 firefox, thunderbird Red Hat Enterprise Linux 7 firefox, thunderbird Red Hat Enterprise Linux 8 firefox, thunderbird Red Hat Enterprise Linux 9 firefox, firefox-x11, thunderbird Red Hat Enterprise Linux 10 firefox, thunderbird, rhel10/firefox-flatpak, rhel10/thunderbird-flatpak
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.56% chance of exploitation in the next 30 days, higher than 46% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CNA 3.1 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird

Classification

Weakness
  • CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.