Input validation error in Mozilla Thunderbird - CVE-2025-3909

Vulnerability identifier: #VU109192

CSH Severity: High

CVSS v4: 8.5 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2025-3909

CWE-ID: CWE-20

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to execute arbitrary JavaScript code.

The vulnerability exists due to incorrect handling of the X-Mozilla-External-Attachment-URL header. A remote attacker can create a nested email attachment, set its content type to application/pdf and force the application to execute arbitrary JavaScript code in the file:/// context.

Mozilla Thunderbird
Debian Linux
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Workstation Extension 15
Red Hat Enterprise Linux for ARM 64
Anolis OS
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
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 IBM z Systems - Extended Update Support
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Slackware Linux
SUSE Package Hub 15
openSUSE Leap
Ubuntu
openEuler
Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions
mozilla-thunderbird
thunderbird (Debian package)
thunderbird (Red Hat package)
MozillaThunderbird-translations-other
MozillaThunderbird-translations-common
MozillaThunderbird-debuginfo
MozillaThunderbird
MozillaThunderbird-debugsource
thunderbird
thunderbird-debuginfo
thunderbird-debugsource
thunderbird-librnp-rnp
thunderbird-wayland
thunderbird (Ubuntu package)

Install updates from vendor's website.

Mozilla Thunderbird - addressed in versions 128.10.1, 138.0.1
mozilla-thunderbird - update to 128.10.1esr
thunderbird (Debian package) - update to 1:128.10.1esr-1~deb12u1
thunderbird (Red Hat package) - addressed in versions 128.10.1-1.el8_2, 128.10.1-1.el8_4, 128.10.1-1.el8_6, 128.10.1-1.el8_8, 128.10.1-1.el9_2, 128.10.1-1.el10_0, 128.11.0-1.el8_10
MozillaThunderbird-translations-other - update to 128.10.1-150200.8.215.1
MozillaThunderbird-translations-common - update to 128.10.1-150200.8.215.1
MozillaThunderbird-debuginfo - update to 128.10.1-150200.8.215.1
MozillaThunderbird - update to 128.10.1-150200.8.215.1
MozillaThunderbird-debugsource - update to 128.10.1-150200.8.215.1
thunderbird - update to 128.11.0-1.0.1
thunderbird - update to 128.11.1-1
thunderbird-debuginfo - update to 128.11.1-1
thunderbird-debugsource - update to 128.11.1-1
thunderbird-librnp-rnp - update to 128.11.1-1
thunderbird-wayland - update to 128.11.1-1
thunderbird (Ubuntu package) - update to 1:128.12.0+build1-0ubuntu0.22.04.1

• https://www.mozilla.org/en-US/security/advisories/mfsa2025-34/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1958376
• https://www.mozilla.org/en-US/security/advisories/mfsa2025-35/

• Multiple vulnerabilities in Mozilla Thunderbird
• Slackware Linux update for mozilla-thunderbird
• Debian update for thunderbird
• SUSE update for MozillaThunderbird
• Red Hat Enterprise Linux 10 update for thunderbird
• SUSE update for MozillaThunderbird
• Red Hat Enterprise Linux 9 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Anolis OS update for thunderbird
• openEuler 24.03 LTS SP2 update for thunderbird
• Ubuntu update for thunderbird