critical 9.6

CVE-2026-100778 json

Sandbox escape due to use-after-free in the DOM: Core & HTML component

published 2026-09-29 41 d ago modified 2026-10-05 34 d ago also EUVD-2026-88930

cvss: 9.6; 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 25%
public exploits: 0; none known

Sandbox escape due to use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

Patch / fix

fixed in 4 distros 5

mozilla firefox 115.42, 140.17, 153.4, 157
mozilla firefox_esr 115.42, 140.17, 153.4, 157
mozilla thunderbird 140.17, 153.4, 157
mozilla thunderbird_esr 140.17, 153.4, 157

debian suse opensuse almalinux rocky linux

firefox-esr Debian 12 153.4.0esr-1~deb12u1
firefox-esr Debian 13 153.4.0esr-1~deb13u1
firefox-esr Debian 14 153.4.0esr-1
thunderbird Debian 12 1:140.17.0esr-1~deb12u1
thunderbird Debian 13 1:140.17.0esr-1~deb13u1
thunderbird Debian 14 1:153.4.0esr-1

debian advisories DEBIAN-CVE-2026-100778

MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 153.4.0-150400.13.6.1
MozillaFirefox SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 153.4.0-150400.157.11.1
MozillaFirefox SLES for SAP applications 16.0, SLES 16.0 153.4.0-160000.1.1
MozillaFirefox SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 153.4.0-118.11.1

suse advisories SUSE-SU-2026:4627-1 SUSE-SU-2026:4545-1 SUSE-SU-2026:4543-1 SUSE-SU-2026:23981-1

MozillaFirefox openSUSE Tumbleweed 157.0.1-1.1
MozillaThunderbird openSUSE Tumbleweed 153.4.0-1.1
MozillaFirefox openSUSE Leap 16.0 153.4.0-160000.1.1
firefox-esr openSUSE Tumbleweed 153.4.0-1.1

opensuse advisories openSUSE-SU-2026:12097-1 openSUSE-SU-2026:12098-1 openSUSE-SU-2026:21980-1 openSUSE-SU-2026:11917-1

thunderbird AlmaLinux 8 140.17.0-1.el8_10.alma.1
thunderbird AlmaLinux 10 140.17.0-1.el10_2.alma.1
thunderbird AlmaLinux 9 140.17.0-1.el9_8.alma.1
firefox AlmaLinux 9 140.17.0-1.el9_8.alma.1
firefox-x11 AlmaLinux 9 140.17.0-1.el9_8.alma.1
firefox AlmaLinux 10 140.17.0-1.el10_2
firefox AlmaLinux 8 140.17.0-1.el8_10.alma.1

almalinux advisories ALSA-2026:90913 ALSA-2026:80674 ALSA-2026:80694 ALSA-2026:76761 ALSA-2026:76764 ALSA-2026:76850

thunderbird Rocky Linux 8 140.17.0-1.el8_10
firefox Rocky Linux 10 140.17.0-1.el10_2
thunderbird Rocky Linux 10 140.17.0-1.el10_2
firefox Rocky Linux 9 140.17.0-1.el9_8
thunderbird Rocky Linux 9 140.17.0-1.el9_8
firefox Rocky Linux 8 140.17.0-1.el8_10

rocky linux advisories RLSA-2026:90913 RLSA-2026:76764 RLSA-2026:80674 RLSA-2026:76761 RLSA-2026:80694 RLSA-2026:76850

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-2026-100778 updated 2026-11-04 cvss 7.5

firefox: Sandbox escape due to use-after-free in the DOM: Core & HTML component

Red Hat Enterprise Linux 6 firefox, thunderbird Red Hat Enterprise Linux 7 thunderbird
affected: workaround, no fix planned “Out of support scope”
Red Hat Enterprise Linux 10 rhel10/firefox-flatpak, rhel10/thunderbird-flatpak
affected: workaround, no fix available
Red Hat Enterprise Linux AppStream (v. 8) firefox 140.17.0-1.el8_10, thunderbird 140.17.0-1.el8_10
fixed: vendor fix RHSA-2026:76850
Red Hat Enterprise Linux AppStream (v. 9) firefox 140.17.0-1.el9_8, firefox-x11 140.17.0-1.el9_8, thunderbird 140.17.0-1.el9_8
fixed: vendor fix RHSA-2026:76761
Red Hat Enterprise Linux AppStream (v. 10) firefox 140.17.0-1.el10_2, thunderbird 140.17.0-1.el10_2
fixed: vendor fix RHSA-2026:76764
Red Hat Enterprise Linux AppStream AUS (v.8.4) firefox 140.17.0-1.el8_4, thunderbird 140.17.0-1.el8_4
fixed: vendor fix RHSA-2026:92011
Red Hat Enterprise Linux AppStream AUS (v.8.6) firefox 140.17.0-1.el8_6, thunderbird 140.17.0-1.el8_6
fixed: vendor fix RHSA-2026:92228
Red Hat Enterprise Linux AppStream E4S (v.8.8) firefox 140.17.0-1.el8_8, thunderbird 140.17.0-1.el8_8
fixed: vendor fix RHSA-2026:92327

show 8 more

Red Hat Enterprise Linux AppStream E4S (v.9.2) firefox 140.17.0-1.el9_2, firefox-x11 140.17.0-1.el9_2, thunderbird 140.17.0-1.el9_2
fixed: vendor fix RHSA-2026:92226
Red Hat Enterprise Linux AppStream E4S (v.9.4) firefox 140.17.0-1.el9_4, firefox-x11 140.17.0-1.el9_4, thunderbird 140.17.0-1.el9_4
fixed: vendor fix RHSA-2026:92012
Red Hat Enterprise Linux AppStream EUS (v. 10.0) firefox 140.17.0-1.el10_0, thunderbird 140.17.0-1.el10_0
fixed: vendor fix RHSA-2026:92227
Red Hat Enterprise Linux AppStream EUS (v.9.6) firefox 140.17.0-1.el9_6, firefox-x11 140.17.0-1.el9_6, thunderbird 140.17.0-1.el9_6
fixed: vendor fix RHSA-2026:92335
Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) firefox 140.17.0-1.el8_4, thunderbird 140.17.0-1.el8_4
fixed: vendor fix RHSA-2026:92011
Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) firefox 140.17.0-1.el8_6, thunderbird 140.17.0-1.el8_6
fixed: vendor fix RHSA-2026:92228
Red Hat Enterprise Linux AppStream TUS (v.8.8) firefox 140.17.0-1.el8_8, thunderbird 140.17.0-1.el8_8
fixed: vendor fix RHSA-2026:92327
Red Hat Enterprise Linux Server (v. 7 ELS) firefox 140.17.0-1.el7_9
fixed: vendor fix RHSA-2026:92363

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: 40 d ago (2026-09-29)

Exploit prediction

0.32% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	9.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
CNA	3.1	9.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Affected products

Mozilla Firefox
Mozilla Thunderbird

Classification

Weakness

CWE-416 Use After Free

References

mozilla.org /security/advisories/mfsa2026-100/
vendor-advisory
mozilla.org /security/advisories/mfsa2026-101/
vendor-advisory
mozilla.org /security/advisories/mfsa2026-102/
vendor-advisory
mozilla.org /security/advisories/mfsa2026-103/
vendor-advisory
mozilla.org /security/advisories/mfsa2026-97/
vendor-advisory
mozilla.org /security/advisories/mfsa2026-98/
vendor-advisory
mozilla.org /security/advisories/mfsa2026-99/
vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=2068406
permissions-required

Sources

CVE List CVE-2026-100778
NVD CVE-2026-100778

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.

Summary