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Fencer Vulns
high 8.8

CVE-2026-109778 json

Privilege escalation in the WebExtensions component

published 2026-10-13 27 d ago modified 2026-10-14 26 d ago also EUVD-2026-98538

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 20%
public exploits
0
none known

Summary

Privilege escalation in the WebExtensions component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.

Patch / fix

  • mozilla firefox 153.5, 158
  • mozilla firefox_esr 153.5, 158
  • mozilla thunderbird 153.5, 158
  • mozilla thunderbird_esr 153.5, 158
  • firefox-esr Debian 12 153.5.0esr-1~deb12u1
  • firefox-esr Debian 13 153.5.0esr-1~deb13u1
  • firefox-esr Debian 14 153.5.0esr-1
  • thunderbird Debian 12 1:153.5.1esr-1~deb12u1
  • thunderbird Debian 13 1:153.5.1esr-1~deb13u1
  • thunderbird Debian 14 1:153.5.0esr-1

debian advisories DEBIAN-CVE-2026-109778

  • MozillaFirefox SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 153.5.0-150400.157.16.1
  • MozillaFirefox SLES for SAP applications 16.0, SLES 16.0 153.5.0-160000.1.1
  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 153.5.0-150400.13.9.1
  • MozillaFirefox SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 153.5.0-118.16.2

suse advisories SUSE-SU-2026:4834-1SUSE-SU-2026:4806-1SUSE-SU-2026:24260-1SUSE-SU-2026:4736-1

  • MozillaThunderbird openSUSE Tumbleweed 153.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 158.0-1.1
  • MozillaFirefox openSUSE Leap 16.0 153.5.0-160000.1.1
  • firefox-esr openSUSE Tumbleweed 153.5.0-1.1

opensuse advisories openSUSE-SU-2026:12224-1openSUSE-SU-2026:12190-1openSUSE-SU-2026:22139-1openSUSE-SU-2026:12116-1

  • thunderbird AlmaLinux 9 153.5.0-1.el9_8.alma.1

almalinux advisories ALSA-2026:93443

  • thunderbird Rocky Linux 9 153.5.0-1.el9_8

rocky linux advisories RLSA-2026:93443

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-2026-109778 updated cvss 3.4

firefox: Privilege escalation in the WebExtensions component

  • Red Hat Enterprise Linux 6 firefox, thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 firefox, thunderbird
    affected: no fix available, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 firefox, thunderbird Red Hat Enterprise Linux 9 firefox, firefox-x11 Red Hat Enterprise Linux 10 firefox, thunderbird, rhel10/firefox-flatpak, rhel10/thunderbird-flatpak
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 9) thunderbird 153.5.0-1.el9_8
    fixed: vendor fix RHSA-2026:93443
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) thunderbird 153.5.0-1.el9_4
    fixed: vendor fix RHSA-2026:95597
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) thunderbird 153.5.0-1.el9_6
    fixed: vendor fix RHSA-2026:95596

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
no
Technical impact
total
Assessed
27 d ago

Exploit prediction

0.28% chance of exploitation in the next 30 days, higher than 20% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird

Classification

Weakness
  • CWE-269 Improper Privilege Management

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.