Protection mechanism failure in Mozilla products - CVE-2026-16387

Vulnerability identifier: #VU138988

CSH Severity: High

CVSS v4: 7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-16387

CWE-ID: CWE-693

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to bypass site isolation.

The vulnerability exists due to a site isolation issue in the Networking component when handling network operations. A remote attacker can trigger crafted network behavior to bypass site isolation.

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

Install security update from vendor's website.

Firefox for Android - update to 153.0
Mozilla Firefox - update to 153.0
Firefox ESR - update to 140.13.0
Mozilla Thunderbird - addressed in versions 140.13.0, 153.0
firefox-esr (Debian package) - update to 140.13.0esr-1~deb13u1
thunderbird (Debian package) - update to 1:140.13.0esr-2~deb13u1
thunderbird - update to 140.13.0-1
thunderbird-debuginfo - update to 140.13.0-1
thunderbird-debugsource - update to 140.13.0-1
thunderbird-librnp-rnp - update to 140.13.0-1
thunderbird-wayland - update to 140.13.0-1
thunderbird (Red Hat package) - addressed in versions 140.13.0-1.el8_10, 140.13.0-1.el9_2, 140.13.0-1.el9_6, 140.13.0-1.el9_8, 140.13.0-1.el10_0, 140.13.0-1.el10_2
thunderbird - update to 140.13.0-1.0.1
firefox-debugsource - update to 140.13.0-2
firefox-debuginfo - update to 140.13.0-2
firefox - update to 140.13.0-2
MozillaFirefox - addressed in versions 140.13.0-112.324.2, 140.13.0-150200.152.248.1
MozillaFirefox-debuginfo - addressed in versions 140.13.0-112.324.2, 140.13.0-150200.152.248.1
MozillaFirefox-debugsource - addressed in versions 140.13.0-112.324.2, 140.13.0-150200.152.248.1
MozillaFirefox-devel - addressed in versions 140.13.0-112.324.2, 140.13.0-150200.152.248.1
MozillaFirefox-translations-common - addressed in versions 140.13.0-112.324.2, 140.13.0-150200.152.248.1
MozillaThunderbird-debugsource - update to 140.13.0-150200.8.280.1
MozillaThunderbird - update to 140.13.0-150200.8.280.1
MozillaThunderbird-translations-other - update to 140.13.0-150200.8.280.1
MozillaThunderbird-translations-common - update to 140.13.0-150200.8.280.1
MozillaThunderbird-debuginfo - update to 140.13.0-150200.8.280.1
MozillaFirefox-translations-other - update to 140.13.0-150200.152.248.1

• https://www.mozilla.org/en-US/security/advisories/mfsa2026-70/
• https://www.mozilla.org/en-US/security/advisories/mfsa2026-68/
• https://bugzilla.mozilla.org/show_bug.cgi?id=2043200

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