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Fencer Vulns
medium 6.5

CVE-2021-43528 json

Thunderbird unexpectedly enabled JavaScript in the composition area.

published 2021-12-08 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-30457

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.3%
EPSS 1.3% chance of exploitation in 30 days, percentile 70%
public exploits
0
none known

Summary

Thunderbird unexpectedly enabled JavaScript in the composition area. The JavaScript execution context was limited to this area and did not receive chrome-level privileges, but could be used as a stepping stone to further an attack with other vulnerabilities. This vulnerability affects Thunderbird < 91.4.0.

Patch / fix

  • Mozilla Thunderbird 91.4.0
  • thunderbird Debian 14, Debian 13, Debian 12 1:91.4.0-1

debian advisories DEBIAN-CVE-2021-43528

  • thunderbird Ubuntu 18.04 LTS 1:91.5.0+build1-0ubuntu0.18.04.1
  • thunderbird Ubuntu 20.04 LTS 1:91.5.0+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-43528

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • thunderbird RHEL 8 91.4.0-2.el8_5
  • thunderbird RHEL 7 91.4.0-3.el7_9
  • thunderbird RHEL 8.1 E4S 91.4.0-2.el8_1
  • thunderbird RHEL 8.2 EUS 91.4.0-2.el8_2
  • thunderbird RHEL 8.4 EUS 91.4.0-2.el8_4

red hat advisories RHSA-2021:5055RHSA-2021:5047RHSA-2021:5048RHSA-2021:5045RHSA-2021:5046

  • MozillaThunderbird SLE Workstation Extension 15 SP3, SLE Workstation Extension 15 SP2 91.4.0-8.45.2

suse advisories SUSE-SU-2021:4150-1

  • MozillaThunderbird openSUSE Tumbleweed 91.4.0-1.1
  • MozillaThunderbird openSUSE Leap 15.2 91.4.0-lp152.2.52.1
  • MozillaThunderbird openSUSE Leap 15.3 91.4.0-8.45.2

opensuse advisories openSUSE-SU-2024:11670-1openSUSE-SU-2021:1635-1openSUSE-SU-2021:4150-1

  • thunderbird AlmaLinux 8 91.4.0-2.el8_5.alma
  • thunderbird AlmaLinux 8 91.4.0-2.el8_5.alma.plus

almalinux advisories ALSA-2021:5045

  • thunderbird Rocky Linux 8 91.4.0-2.el8_5

rocky linux advisories RLSA-2021:5045

  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 91.4.0-r0

alpine advisories ALPINE-CVE-2021-43528

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • thunderbird Arch Linux 91.4.0-1

arch linux advisories AVG-2608

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-2021-43528 updated cvss 6.3

Mozilla: JavaScript unexpectedly enabled for the composition area

  • Red Hat Enterprise Linux 6 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) thunderbird 91.4.0-2.el8_5
    fixed: vendor fix RHSA-2021:5045
  • Red Hat Enterprise Linux AppStream E4S (v. 8.1) thunderbird 91.4.0-2.el8_1
    fixed: vendor fix RHSA-2021:5055
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird 91.4.0-2.el8_2
    fixed: vendor fix RHSA-2021:5047
  • Red Hat Enterprise Linux AppStream EUS (v.8.4) thunderbird 91.4.0-2.el8_4
    fixed: vendor fix RHSA-2021:5048
  • Red Hat Enterprise Linux Client (v. 7) thunderbird 91.4.0-3.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) thunderbird 91.4.0-3.el7_9 Red Hat Enterprise Linux Workstation (v. 7) thunderbird 91.4.0-3.el7_9
    fixed: vendor fix RHSA-2021:5046

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

Exploit prediction

1.31% chance of exploitation in the next 30 days, higher than 70% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

  • Mozilla Thunderbird

Classification

Weakness
  • CWE-269 Improper Privilege Management

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.