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Fencer Vulns
high 7.5

CVE-2026-14899 json

Off-by-one out of bounds read in MIME header parser for forwarding

published 2026-07-22 3 mo ago modified 2026-10-24 15 d ago also EUVD-2026-47773

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

The code to parse MIME headers for display when forwarding a message (if the setting to view all headers was enabled) had an off-by-one error, allowing a single byte to be read from the memory after the buffer for the headers, and potentially crashing Thunderbird. This vulnerability was fixed in Thunderbird 153 and Thunderbird 140.13.

Patch / fix

  • mozilla thunderbird 140.13, 153
  • mozilla thunderbird_esr 140.13, 153
  • thunderbird Debian 12 1:140.13.0esr-2~deb12u1
  • thunderbird Debian 13 1:140.13.0esr-2~deb13u1
  • thunderbird Debian 14 1:140.13.0esr-1

debian advisories DEBIAN-CVE-2026-14899

  • thunderbird RHEL 8 140.13.0-1.el8_10
  • thunderbird RHEL 9 140.13.0-1.el9_8
  • thunderbird RHEL 10.2 140.13.0-1.el10_2
  • thunderbird RHEL 9.2 E4S 140.13.0-1.el9_2
  • thunderbird RHEL 8.8 TUS, RHEL 8.8 E4S 140.13.0-1.el8_8
  • thunderbird RHEL 8.4 EUS_LONG_LIFE, RHEL 8.4 AUS 140.13.0-1.el8_4
  • thunderbird RHEL 8.6 EUS_LONG_LIFE, RHEL 8.6 AUS 140.13.0-1.el8_6
  • thunderbird enterprise linux eus 10.0 140.13.0-1.el10_0

red hat advisories RHSA-2026:53475RHSA-2026:53454RHSA-2026:53455RHSA-2026:53453RHSA-2026:53445RHSA-2026:53446

  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 153.2.0-150400.13.3.1
  • MozillaThunderbird SLE Workstation Extension 15 SP7, SLE Module for Package Hub 15 SP7 140.13.0-150200.8.280.1

suse advisories SUSE-SU-2026:4268-1SUSE-SU-2026:3546-1

  • MozillaThunderbird openSUSE Tumbleweed 140.13.0-1.1

opensuse advisories openSUSE-SU-2026:11359-1

  • thunderbird AlmaLinux 9 140.13.0-1.el9_8.alma.1
  • thunderbird AlmaLinux 8 140.13.0-1.el8_10.alma.1
  • thunderbird AlmaLinux 10 140.13.0-1.el10_2.alma.1

almalinux advisories ALSA-2026:49921ALSA-2026:49922ALSA-2026:49621

  • thunderbird Rocky Linux 10 140.13.0-1.el10_2
  • thunderbird Rocky Linux 9 140.13.0-1.el9_8
  • thunderbird Rocky Linux 8 140.13.0-1.el8_10

rocky linux advisories RLSA-2026:49621RLSA-2026:49921RLSA-2026:49922

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-2026-14899 updated cvss 6.1

thunderbird: Off-by-one out of bounds read in MIME header parser for forwarding

  • Red Hat Enterprise Linux 6 thunderbird Red Hat Enterprise Linux 7 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 10 rhel10/thunderbird-flatpak
    affected: no fix available
  • Red Hat Enterprise Linux AppStream (v. 8) thunderbird 140.13.0-1.el8_10
    fixed: vendor fix RHSA-2026:49922
  • Red Hat Enterprise Linux AppStream (v. 9) thunderbird 140.13.0-1.el9_8
    fixed: vendor fix RHSA-2026:49921
  • Red Hat Enterprise Linux AppStream (v. 10) thunderbird 140.13.0-1.el10_2
    fixed: vendor fix RHSA-2026:49621
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) thunderbird 140.13.0-1.el8_4
    fixed: vendor fix RHSA-2026:53455
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) thunderbird 140.13.0-1.el8_6
    fixed: vendor fix RHSA-2026:53453
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) thunderbird 140.13.0-1.el8_8
    fixed: vendor fix RHSA-2026:53454
show 7 more
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) thunderbird 140.13.0-1.el9_2
    fixed: vendor fix RHSA-2026:53475
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) thunderbird 140.13.0-1.el9_4
    fixed: vendor fix RHSA-2026:53444
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) thunderbird 140.13.0-1.el10_0
    fixed: vendor fix RHSA-2026:53445
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) thunderbird 140.13.0-1.el9_6
    fixed: vendor fix RHSA-2026:53446
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) thunderbird 140.13.0-1.el8_4
    fixed: vendor fix RHSA-2026:53455
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) thunderbird 140.13.0-1.el8_6
    fixed: vendor fix RHSA-2026:53453
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) thunderbird 140.13.0-1.el8_8
    fixed: vendor fix RHSA-2026:53454

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
yes
Technical impact
partial
Assessed
3 mo ago

Exploit prediction

0.47% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

  • Mozilla Thunderbird

Classification

Weakness

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.

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