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Fencer Vulns
high 7.5

CVE-2026-84640 json

One byte overflow read in mail parser

published 2026-09-01 2 mo ago modified 2026-09-03 2 mo ago also EUVD-2026-69709

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 18%
public exploits
0
none known

Summary

A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Patch / fix

  • mozilla thunderbird 140.15.0, 153.2.0, 155.0
  • thunderbird Debian 12 1:140.15.0esr-1~deb12u1
  • thunderbird Debian 13 1:140.15.0esr-1~deb13u1
  • thunderbird Debian 14 1:153.2.0esr-1

debian advisories DEBIAN-CVE-2026-84640

  • thunderbird RHEL 8 140.16.0-1.el8_10
  • thunderbird RHEL 10.2 140.16.0-1.el10_2
  • thunderbird RHEL 9 140.16.0-1.el9_8
  • thunderbird RHEL 8.4 EUS_LONG_LIFE, RHEL 8.4 AUS 140.16.0-1.el8_4
  • thunderbird RHEL 8.6 EUS_LONG_LIFE, RHEL 8.6 AUS 140.16.0-1.el8_6
  • thunderbird RHEL 8.8 TUS, RHEL 8.8 E4S 140.16.0-1.el8_8
  • thunderbird RHEL 9.6 EUS 140.15.0-1.el9_6
  • thunderbird RHEL 9.2 E4S 140.15.0-1.el9_2

red hat advisories RHSA-2026:82122RHSA-2026:81913RHSA-2026:81912RHSA-2026:80503RHSA-2026:77632RHSA-2026:77631

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

suse advisories SUSE-SU-2026:4268-1

  • MozillaThunderbird openSUSE Tumbleweed 140.15.0-1.1

opensuse advisories openSUSE-SU-2026:11678-1

  • thunderbird AlmaLinux 8 140.16.0-1.el8_10.alma.1
  • thunderbird AlmaLinux 10 140.16.0-1.el10_2.alma.1
  • thunderbird AlmaLinux 9 140.16.0-1.el9_8.alma.1

almalinux advisories ALSA-2026:73971ALSA-2026:73130ALSA-2026:70642

  • thunderbird Rocky Linux 8 140.16.0-1.el8_10
  • thunderbird Rocky Linux 10 140.16.0-1.el10_2
  • thunderbird Rocky Linux 9 140.16.0-1.el9_8

rocky linux advisories RLSA-2026:73971RLSA-2026:73130RLSA-2026:70642

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-2026-84640 updated cvss 6.1

thunderbird: One byte overflow read in mail parser

  • 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 140.16.0-1.el8_10
    fixed: vendor fix RHSA-2026:73971
  • Red Hat Enterprise Linux AppStream (v. 9) thunderbird 140.16.0-1.el9_8
    fixed: vendor fix RHSA-2026:70642
  • Red Hat Enterprise Linux AppStream (v. 10) thunderbird 140.16.0-1.el10_2
    fixed: vendor fix RHSA-2026:73130
  • Red Hat Enterprise Linux AppStream AUS (v.8.4) thunderbird 140.16.0-1.el8_4
    fixed: vendor fix RHSA-2026:82122
  • Red Hat Enterprise Linux AppStream AUS (v.8.6) thunderbird 140.16.0-1.el8_6
    fixed: vendor fix RHSA-2026:81913
  • Red Hat Enterprise Linux AppStream E4S (v.8.8) thunderbird 140.16.0-1.el8_8
    fixed: vendor fix RHSA-2026:81912
show 7 more
  • Red Hat Enterprise Linux AppStream E4S (v.9.2) thunderbird 140.15.0-1.el9_2
    fixed: vendor fix RHSA-2026:77632
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) thunderbird 140.15.0-1.el9_4
    fixed: vendor fix RHSA-2026:77627
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) thunderbird 140.15.0-1.el10_0
    fixed: vendor fix RHSA-2026:77631
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) thunderbird 140.15.0-1.el9_6
    fixed: vendor fix RHSA-2026:80503
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.4) thunderbird 140.16.0-1.el8_4
    fixed: vendor fix RHSA-2026:82122
  • Red Hat Enterprise Linux AppStream EUS EXTENSION (v.8.6) thunderbird 140.16.0-1.el8_6
    fixed: vendor fix RHSA-2026:81913
  • Red Hat Enterprise Linux AppStream TUS (v.8.8) thunderbird 140.16.0-1.el8_8
    fixed: vendor fix RHSA-2026:81912

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
2 mo ago

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 18% 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.