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Fencer Intel
high 8.2

CVE-2026-4371 json

Out of bounds read in IMAP parsing

published 7mo ago modified 3mo 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

Is CVE-2026-4371 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

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
7mo ago

Exploit prediction

0.37% chance of exploitation in the next 30 days, higher than 30% of all scored CVEs (FIRST EPSS, 2026-11-09).

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 Intel 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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.