Use-after-free in Mozilla products - CVE-2026-84121

Vulnerability identifier: #VU146608

CSH Severity: High

CVSS v4: 8.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-84121

CWE-ID: CWE-416

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to escape the sandbox.

The vulnerability exists due to use-after-free in DOM: Security component when processing web content. A remote attacker can convince the victim to visit a specially crafted website to escape the sandbox.

User interaction is required.

Mozilla Firefox
Firefox ESR
Firefox for Android
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 12 SP5 LTSS Extended
SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server 15 SP6
Debian Linux
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise High Performance Computing 12
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server for SAP Applications 12
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Micro
SUSE Linux Enterprise Micro for Rancher
Red Hat Enterprise Linux for ARM 64
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux Server - AUS
Desktop Applications Module
Basesystem Module
openSUSE Leap
openEuler
rust-cbindgen-debuginfo
rust-cbindgen
rust-cbindgen-debugsource
libfreebl3
mozilla-nss-debugsource
mozilla-nss-devel
mozilla-nss-certs-debuginfo
libsoftokn3
libfreebl3-debuginfo
mozilla-nss
mozilla-nss-tools
mozilla-nss-certs
mozilla-nss-sysinit-debuginfo
mozilla-nss-sysinit
libsoftokn3-debuginfo
libfreebl3-32bit
libfreebl3-debuginfo-32bit
mozilla-nss-tools-debuginfo
mozilla-nss-sysinit-debuginfo-32bit
mozilla-nss-32bit
libsoftokn3-debuginfo-32bit
mozilla-nss-certs-debuginfo-32bit
mozilla-nss-debuginfo
libsoftokn3-32bit
mozilla-nss-certs-32bit
mozilla-nss-sysinit-32bit
mozilla-nss-debuginfo-32bit
libsoftokn3-64bit
mozilla-nss-sysinit-32bit-debuginfo
libsoftokn3-32bit-debuginfo
mozilla-nss-32bit-debuginfo
libfreebl3-32bit-debuginfo
mozilla-nss-certs-64bit-debuginfo
mozilla-nss-sysinit-64bit-debuginfo
mozilla-nss-certs-64bit
mozilla-nss-sysinit-64bit
libsoftokn3-64bit-debuginfo
libfreebl3-64bit-debuginfo
libfreebl3-64bit
mozilla-nss-64bit-debuginfo
mozilla-nss-64bit
mozilla-nss-certs-32bit-debuginfo
mozilla-nspr-32bit
mozilla-nspr
mozilla-nspr-debugsource
mozilla-nspr-debuginfo-32bit
mozilla-nspr-debuginfo
mozilla-nspr-devel
mozilla-nspr-64bit-debuginfo
mozilla-nspr-64bit
mozilla-nspr-32bit-debuginfo
firefox
firefox-debuginfo
firefox-debugsource
firefox (Red Hat package)
MozillaFirefox-branding-SLE
MozillaFirefox-debugsource
MozillaFirefox-translations-common
MozillaFirefox-devel
MozillaFirefox-debuginfo
MozillaFirefox
MozillaFirefox-branding-upstream
MozillaFirefox-translations-other
firefox-esr (Debian package)

Install security update from vendor's website.

Mozilla Firefox - update to 155.0
Firefox for Android - update to 155.0
Firefox ESR - addressed in versions 115.40.0, 140.15.0, 153.2.0
rust-cbindgen-debuginfo - update to 0.29.4+git0-150400.11.3.2
rust-cbindgen - update to 0.29.4+git0-150400.11.3.2
rust-cbindgen-debugsource - update to 0.29.4+git0-150400.11.3.2
libfreebl3 - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-debugsource - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-devel - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-certs-debuginfo - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
libsoftokn3 - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
libfreebl3-debuginfo - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-tools - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-certs - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-sysinit-debuginfo - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-sysinit - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
libsoftokn3-debuginfo - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
libfreebl3-32bit - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
libfreebl3-debuginfo-32bit - update to 3.125-58.147.1
mozilla-nss-tools-debuginfo - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-sysinit-debuginfo-32bit - update to 3.125-58.147.1
mozilla-nss-32bit - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
libsoftokn3-debuginfo-32bit - update to 3.125-58.147.1
mozilla-nss-certs-debuginfo-32bit - update to 3.125-58.147.1
mozilla-nss-debuginfo - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
libsoftokn3-32bit - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-certs-32bit - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-sysinit-32bit - addressed in versions 3.125-58.147.1, 3.125-150400.3.74.1
mozilla-nss-debuginfo-32bit - update to 3.125-58.147.1
libsoftokn3-64bit - update to 3.125-150400.3.74.1
mozilla-nss-sysinit-32bit-debuginfo - update to 3.125-150400.3.74.1
libsoftokn3-32bit-debuginfo - update to 3.125-150400.3.74.1
mozilla-nss-32bit-debuginfo - update to 3.125-150400.3.74.1
libfreebl3-32bit-debuginfo - update to 3.125-150400.3.74.1
mozilla-nss-certs-64bit-debuginfo - update to 3.125-150400.3.74.1
mozilla-nss-sysinit-64bit-debuginfo - update to 3.125-150400.3.74.1
mozilla-nss-certs-64bit - update to 3.125-150400.3.74.1
mozilla-nss-sysinit-64bit - update to 3.125-150400.3.74.1
libsoftokn3-64bit-debuginfo - update to 3.125-150400.3.74.1
libfreebl3-64bit-debuginfo - update to 3.125-150400.3.74.1
libfreebl3-64bit - update to 3.125-150400.3.74.1
mozilla-nss-64bit-debuginfo - update to 3.125-150400.3.74.1
mozilla-nss-64bit - update to 3.125-150400.3.74.1
mozilla-nss-certs-32bit-debuginfo - update to 3.125-150400.3.74.1
mozilla-nspr-32bit - addressed in versions 4.39-19.39.1, 4.39-150400.12.3.1
mozilla-nspr - addressed in versions 4.39-19.39.1, 4.39-150400.12.3.1
mozilla-nspr-debugsource - addressed in versions 4.39-19.39.1, 4.39-150400.12.3.1
mozilla-nspr-debuginfo-32bit - update to 4.39-19.39.1
mozilla-nspr-debuginfo - addressed in versions 4.39-19.39.1, 4.39-150400.12.3.1
mozilla-nspr-devel - addressed in versions 4.39-19.39.1, 4.39-150400.12.3.1
mozilla-nspr-64bit-debuginfo - update to 4.39-150400.12.3.1
mozilla-nspr-64bit - update to 4.39-150400.12.3.1
mozilla-nspr-32bit-debuginfo - update to 4.39-150400.12.3.1
firefox - addressed in versions 140.14.0-1, 140.15.0-1
firefox-debuginfo - addressed in versions 140.14.0-1, 140.15.0-1
firefox-debugsource - addressed in versions 140.14.0-1, 140.15.0-1
firefox (Red Hat package) - addressed in versions 140.15.0-1.el8_4, 140.15.0-1.el8_10, 140.15.0-1.el9_8, 140.15.0-1.el10_2
MozillaFirefox-branding-SLE - addressed in versions 153-41.3.8, 153-150400.14.3.1
MozillaFirefox-debugsource - addressed in versions 153.2.0-118.5.4, 153.2.0-150400.157.5.1
MozillaFirefox-translations-common - addressed in versions 153.2.0-118.5.4, 153.2.0-150400.157.5.1
MozillaFirefox-devel - addressed in versions 153.2.0-118.5.4, 153.2.0-150400.157.5.1
MozillaFirefox-debuginfo - addressed in versions 153.2.0-118.5.4, 153.2.0-150400.157.5.1
MozillaFirefox - addressed in versions 153.2.0-118.5.4, 153.2.0-150400.157.5.1
MozillaFirefox-branding-upstream - update to 153.2.0-150400.157.5.1
MozillaFirefox-translations-other - update to 153.2.0-150400.157.5.1
firefox-esr (Debian package) - update to 140.15.0esr-1~deb13u1

• https://www.mozilla.org/en-US/security/advisories/mfsa2026-83/
• https://www.mozilla.org/en-US/security/advisories/mfsa2026-82/
• https://www.mozilla.org/en-US/security/advisories/mfsa2026-84/
• https://www.mozilla.org/en-US/security/advisories/mfsa2026-85/
• https://bugzilla.mozilla.org/show_bug.cgi?id=2059018

• Multiple vulnerabilities in Mozilla Firefox
• Debian update for firefox-esr
• openEuler 22.03 LTS SP4 update for firefox
• openEuler 24.03 LTS SP4 update for firefox
• openEuler 24.03 LTS SP1 update for firefox
• Red Hat Enterprise Linux 10 update for firefox
• Red Hat Enterprise Linux 9 update for firefox
• Red Hat Enterprise Linux 8 update for firefox
• SUSE update for MozillaFirefox, MozillaFirefox-branding-SLE, mozilla-nspr, mozilla-nss, rust-cbindgen
• SUSE update for MozillaFirefox, mozilla-nspr, mozilla-nss, rust-cbindgen
• Red Hat Enterprise Linux 8 update for firefox