Buffer overflow in Mozilla products - CVE-2026-5734

Vulnerability identifier: #VU125090

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-2026-5734

CWE-ID: CWE-119

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to execute arbitrary code on the target system.

The vulnerability exists due to a boundary error when processing HTML content. A remote attacker can trick the victim into visiting a specially crafted website, trigger memory corruption and execute arbitrary code on the target system.

Successful exploitation of this vulnerability may result in complete compromise of vulnerable system.

Firefox for Android
Firefox ESR
Mozilla Firefox
Debian Linux
SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server 12 SP5 LTSS Extended
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing 12
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server for SAP Applications 12
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Workstation Extension 15
SUSE Linux Enterprise Desktop 15
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for ARM 64
Anolis OS
Red Hat Enterprise Linux Server - AUS
Red Hat Enterprise Linux Server - TUS
Red Hat Enterprise Linux for ARM 64 - Extended Update Support
Red Hat Enterprise Linux for Power, little endian - Extended Update Support
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Red Hat Enterprise Linux for IBM z Systems - Extended Update Support
SUSE Package Hub 15
Desktop Applications Module
openEuler
Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions
thunderbird (Debian package)
firefox-esr (Debian package)
firefox-debugsource
firefox
firefox-debuginfo
firefox (Red Hat package)
thunderbird (Red Hat package)
MozillaFirefox-devel
MozillaFirefox
MozillaFirefox-debugsource
MozillaFirefox-translations-common
MozillaFirefox-debuginfo
MozillaThunderbird-debuginfo
MozillaThunderbird-translations-common
MozillaThunderbird
MozillaThunderbird-debugsource
MozillaThunderbird-translations-other
MozillaFirefox-translations-other
thunderbird-debuginfo
thunderbird
thunderbird-debugsource
thunderbird-librnp-rnp
thunderbird-wayland
Mozilla Thunderbird

Install updates from vendor's website.

Firefox for Android - update to 149.0.2
Firefox ESR - update to 140.9.1
Mozilla Firefox - update to 149.0.2
Mozilla Thunderbird - addressed in versions 140.9.1, 149.0.2
thunderbird (Debian package) - addressed in versions 1:140.9.1esr-1~deb12u1, 1:140.9.1esr-1~deb13u1
firefox-esr (Debian package) - addressed in versions 140.9.1esr-1~deb12u1, 140.9.1esr-1~deb13u1
firefox-debugsource - update to 140.9.1-1
firefox - update to 140.9.1-1
firefox-debuginfo - update to 140.9.1-1
firefox (Red Hat package) - addressed in versions 140.9.1-1.el8_2, 140.9.1-1.el8_4, 140.9.1-1.el8_6, 140.9.1-1.el8_8, 140.9.1-1.el8_10, 140.9.1-1.el9_0, 140.9.1-1.el9_2, 140.9.1-1.el9_4, 140.9.1-1.el9_6, 140.9.1-1.el9_7, 140.9.1-1.el10_0, 140.9.1-1.el10_1, 140.9.1-2.el7_9
thunderbird (Red Hat package) - addressed in versions 140.9.1-1.el8_4, 140.9.1-1.el8_6, 140.9.1-1.el8_8, 140.9.1-1.el8_10, 140.9.1-1.el9_0, 140.9.1-1.el9_2, 140.9.1-1.el9_4, 140.9.1-1.el9_6, 140.9.1-1.el9_7, 140.9.1-1.el10_0, 140.9.1-1.el10_1
firefox - update to 140.9.1-1.0.1
MozillaFirefox-devel - addressed in versions 140.9.1-112.307.1, 140.9.1-150200.152.228.1
MozillaFirefox - addressed in versions 140.9.1-112.307.1, 140.9.1-150200.152.228.1
MozillaFirefox-debugsource - addressed in versions 140.9.1-112.307.1, 140.9.1-150200.152.228.1
MozillaFirefox-translations-common - addressed in versions 140.9.1-112.307.1, 140.9.1-150200.152.228.1
MozillaFirefox-debuginfo - addressed in versions 140.9.1-112.307.1, 140.9.1-150200.152.228.1
MozillaThunderbird-debuginfo - update to 140.9.1-150200.8.266.1
MozillaThunderbird-translations-common - update to 140.9.1-150200.8.266.1
MozillaThunderbird - update to 140.9.1-150200.8.266.1
MozillaThunderbird-debugsource - update to 140.9.1-150200.8.266.1
MozillaThunderbird-translations-other - update to 140.9.1-150200.8.266.1
MozillaFirefox-translations-other - update to 140.9.1-150200.152.228.1
thunderbird-debuginfo - update to 140.10.0-1
thunderbird - update to 140.10.0-1
thunderbird-debugsource - update to 140.10.0-1
thunderbird-librnp-rnp - update to 140.10.0-1
thunderbird-wayland - update to 140.10.0-1
thunderbird - update to 140.12.0-1.0.1

• https://www.mozilla.org/en-US/security/advisories/mfsa2026-27/
• https://www.mozilla.org/en-US/security/advisories/mfsa2026-25/
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2022369
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2023026
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2023545
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2023555
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2023958
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2025422
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2025468
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2025492
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=2025505

• Multiple vulnerabilities in Mozilla Firefox
• Multiple vulnerabilities in Thunderbird ESR
• Multiple vulnerabilities in Mozilla Thunderbird
• Debian update for firefox-esr
• openEuler 22.03 LTS SP4 update for firefox
• openEuler 24.03 LTS SP3 update for firefox
• openEuler 24.03 LTS SP2 update for firefox
• openEuler 24.03 LTS SP1 update for firefox
• openEuler 24.03 LTS update for firefox
• Red Hat Enterprise Linux 9 update for firefox
• Red Hat Enterprise Linux 10 update for firefox
• SUSE update for MozillaFirefox
• Red Hat Enterprise Linux 8 update for firefox
• SUSE update for MozillaFirefox
• Debian update for thunderbird
• Red Hat Enterprise Linux 9 update for thunderbird
• SUSE update for MozillaThunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 10 update for thunderbird
• Anolis OS update for firefox
• openEuler 24.03 LTS SP3 update for thunderbird
• Red Hat Enterprise Linux 8 update for firefox
• Red Hat Enterprise Linux 10 update for thunderbird
• Red Hat Enterprise Linux 9 update for thunderbird
• Red Hat Enterprise Linux 9 update for thunderbird
• Red Hat Enterprise Linux 9 update for thunderbird
• Red Hat Enterprise Linux 9 update for thunderbird
• Red Hat Enterprise Linux 9 update for firefox
• Red Hat Enterprise Linux 9 update for firefox
• Red Hat Enterprise Linux 9 update for firefox
• Red Hat Enterprise Linux 8 update for firefox
• Red Hat Enterprise Linux 10 update for firefox
• Red Hat Enterprise Linux 8 update for firefox
• Red Hat Enterprise Linux 8 update for firefox
• Red Hat Enterprise Linux 9 update for firefox
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 7 Extended Lifecycle Support update for firefox
• Red Hat Enterprise Linux 8 update for thunderbird
• Anolis OS update for thunderbird