Skip to content
Fencer Vulns
high 8.2

CVE-2026-4371 json

Out of bounds read in IMAP parsing

published 2026-03-24 7 mo ago modified 2026-07-15 3 mo ago also EUVD-2026-15023

cvss
8.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 30%
public exploits
0
none known

Summary

A malicious mail server could send malformed strings with negative lengths, causing the parser to read memory outside the buffer. If a mail server or connection to a mail server were compromised, an attacker could cause the parser to malfunction, potentially crashing Thunderbird or leaking sensitive data. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 0:140.9.0-1.el10_1
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support 0:140.9.0-1.el10_0
  • Red Hat Red Hat Enterprise Linux 8 0:140.9.0-1.el8_10
  • Red Hat Red Hat Enterprise Linux 8.2 Advanced Update Support 0:140.9.0-1.el8_2
  • Red Hat Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support 0:140.9.0-1.el8_4
  • Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On 0:140.9.0-1.el8_4
  • Red Hat Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support 0:140.9.0-1.el8_6
  • Red Hat Red Hat Enterprise Linux 8.6 Telecommunications Update Service 0:140.9.0-1.el8_6
  • Red Hat Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions 0:140.9.0-1.el8_6
  • Red Hat Red Hat Enterprise Linux 8.8 Telecommunications Update Service 0:140.9.0-1.el8_8
  • Red Hat Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions 0:140.9.0-1.el8_8
  • Red Hat Red Hat Enterprise Linux 9 0:140.9.0-1.el9_7
  • Red Hat Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions 0:140.9.0-1.el9_0
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions 0:140.9.0-1.el9_2
  • Red Hat Red Hat Enterprise Linux 9.4 Extended Update Support 0:140.9.0-1.el9_4
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support 0:140.9.0-1.el9_6
  • thunderbird Debian 12 1:140.9.0esr-1~deb12u1
  • thunderbird Debian 13 1:140.9.0esr-1~deb13u1
  • thunderbird Debian 14 1:140.9.0esr-1

debian advisories DEBIAN-CVE-2026-4371

  • thunderbird RHEL 8 140.9.0-1.el8_10
  • thunderbird RHEL 10.1 140.9.0-1.el10_1
  • thunderbird RHEL 9 140.9.0-1.el9_7
  • thunderbird RHEL 8.4 EUS_LONG_LIFE, RHEL 8.4 AUS 140.9.0-1.el8_4
  • thunderbird enterprise linux eus 10.0 140.9.0-1.el10_0
  • thunderbird RHEL 8.6 TUS, RHEL 8.6 E4S, RHEL 8.6 AUS 140.9.0-1.el8_6
  • thunderbird RHEL 9.4 EUS 140.9.0-1.el9_4
  • thunderbird RHEL 9.2 E4S 140.9.0-1.el9_2

red hat advisories RHSA-2026:8850RHSA-2026:8315RHSA-2026:8289RHSA-2026:8290RHSA-2026:8287RHSA-2026:8288

  • MozillaThunderbird openSUSE Leap 15.6 140.9.0-150200.8.263.1

suse advisories SUSE-SU-2026:1163-1

  • MozillaThunderbird openSUSE Tumbleweed 140.9.0-1.1

opensuse advisories openSUSE-SU-2026:10447-1

  • thunderbird AlmaLinux 8 140.9.0-1.el8_10.alma.1
  • thunderbird AlmaLinux 10 140.9.0-1.el10_1.alma.1
  • thunderbird AlmaLinux 9 140.9.0-1.el9_7.alma.1

almalinux advisories ALSA-2026:6917ALSA-2026:6342ALSA-2026:6188

  • thunderbird Rocky Linux 8 140.9.0-1.el8_10
  • thunderbird Rocky Linux 10 140.9.0-1.el10_1
  • thunderbird Rocky Linux 9 140.9.0-1.el9_7

rocky linux advisories RLSA-2026:6917RLSA-2026:6342RLSA-2026:6188

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-4371 updated cvss 8.2

thunderbird: Out of bounds read in IMAP parsing

  • Red Hat Enterprise Linux 6 thunderbird Red Hat Enterprise Linux 7 thunderbird
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 rhel10/thunderbird-flatpak
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) thunderbird 140.9.0-1.el8_10
    fixed: vendor fix RHSA-2026:6917
  • Red Hat Enterprise Linux AppStream (v. 9) thunderbird 140.9.0-1.el9_7
    fixed: vendor fix RHSA-2026:6188
  • Red Hat Enterprise Linux AppStream (v. 10) thunderbird 140.9.0-1.el10_1
    fixed: vendor fix RHSA-2026:6342
  • Red Hat Enterprise Linux AppStream AUS (v. 8.2) thunderbird 140.9.0-1.el8_2
    fixed: vendor fix RHSA-2026:8285
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) thunderbird 140.9.0-1.el8_4
    fixed: vendor fix RHSA-2026:8850
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) thunderbird 140.9.0-1.el8_6 Red Hat Enterprise Linux AppStream E4S (v.8.6) thunderbird 140.9.0-1.el8_6
    fixed: vendor fix RHSA-2026:8289
show 9 more
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) thunderbird 140.9.0-1.el8_8
    fixed: vendor fix RHSA-2026:8288
  • Red Hat Enterprise Linux AppStream E4S (v.9.0) thunderbird 140.9.0-1.el9_0
    fixed: vendor fix RHSA-2026:8286
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) thunderbird 140.9.0-1.el9_2
    fixed: vendor fix RHSA-2026:8287
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) thunderbird 140.9.0-1.el10_0
    fixed: vendor fix RHSA-2026:8315
  • Red Hat Enterprise Linux AppStream EUS (v.9.4) thunderbird 140.9.0-1.el9_4
    fixed: vendor fix RHSA-2026:8290
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) thunderbird 140.9.0-1.el9_6
    fixed: vendor fix RHSA-2026:8284
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) thunderbird 140.9.0-1.el8_4
    fixed: vendor fix RHSA-2026:8850
  • Red Hat Enterprise Linux AppStream TUS (v.8.6) thunderbird 140.9.0-1.el8_6
    fixed: vendor fix RHSA-2026:8289
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) thunderbird 140.9.0-1.el8_8
    fixed: vendor fix RHSA-2026:8288

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.37% chance of exploitation in the next 30 days, higher than 30% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
CISA ADP 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
CNA 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
CNA 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Affected products

  • Mozilla Thunderbird
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 10.0 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 8.2 Advanced Update Support
  • Red Hat Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support
  • Red Hat Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On
  • Red Hat Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support
  • Red Hat Red Hat Enterprise Linux 8.6 Telecommunications Update Service
  • Red Hat Red Hat Enterprise Linux 8.6 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 8.8 Telecommunications Update Service
  • Red Hat Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Enterprise Linux 9.0 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions
  • Red Hat Red Hat Enterprise Linux 9.4 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 9.6 Extended Update Support
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7

Classification

Weakness
  • CWE-126 Buffer Over-read
  • CWE-130 Improper Handling of Length Parameter Inconsistency

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.