Out-of-bounds read in Mozilla Thunderbird - CVE-2026-4371

Vulnerability identifier: #VU124597

CSH Severity: Low

CVSS v4: 2.1 [CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:A/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N]

CVE-ID: CVE-2026-4371

CWE-ID: CWE-125

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to gain access to potentially sensitive information.

The vulnerability exists due to a boundary condition when reading responses from the IMAP server. A remote attacker with control over a malicious IMAP server can send specially crafted responses to the email client, trigger an out-of-bounds read error and read contents of memory on the system.

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

Install updates from vendor's website.

Mozilla Thunderbird - addressed in versions 140.9.0, 149.0
thunderbird (Debian package) - addressed in versions 1:140.9.0esr-1~deb12u1, 1:140.9.0esr-1~deb13u1
thunderbird (Red Hat package) - addressed in versions 140.9.0-1.el8_2, 140.9.0-1.el8_4, 140.9.0-1.el8_6, 140.9.0-1.el8_8, 140.9.0-1.el9_2, 140.9.0-1.el9_4, 140.9.0-1.el9_6, 140.9.0-1.el10_0, 140.9.0-1.el10_1
MozillaThunderbird-translations-common - update to 140.9.0-150200.8.263.1
MozillaThunderbird-debugsource - update to 140.9.0-150200.8.263.1
MozillaThunderbird-translations-other - update to 140.9.0-150200.8.263.1
MozillaThunderbird - update to 140.9.0-150200.8.263.1
MozillaThunderbird-debuginfo - update to 140.9.0-150200.8.263.1
thunderbird - update to 140.9.1-1
thunderbird-debuginfo - update to 140.9.1-1
thunderbird-debugsource - update to 140.9.1-1
thunderbird-librnp-rnp - update to 140.9.1-1
thunderbird-wayland - update to 140.9.1-1
thunderbird - update to 140.12.0-1.0.1

• https://www.mozilla.org/en-US/security/advisories/mfsa2026-23/
• https://www.mozilla.org/en-US/security/advisories/mfsa2026-24/
• https://bugzilla.mozilla.org/show_bug.cgi?id=2023493

• Multiple vulnerabilities in Thunderbird ESR
• Multiple vulnerabilities in Mozilla Thunderbird
• Debian update for thunderbird
• 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 9 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Red Hat Enterprise Linux 9 update for thunderbird
• Red Hat Enterprise Linux 10 update for thunderbird
• openEuler 24.03 LTS SP3 update for thunderbird
• openEuler 24.03 LTS SP2 update for thunderbird
• Red Hat Enterprise Linux 8 update for thunderbird
• Anolis OS update for thunderbird