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Fencer Vulns
critical 9.8

CVE-2021-43529 json

Thunderbird versions prior to 91.3.0 are vulnerable to the heap overflow described in CVE-2021-43527 when processing S/MIME messages.

published 2023-02-16 3 y ago modified 2026-06-17 4 mo ago also EUVD-2021-30458

cvss
9.8
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

Thunderbird versions prior to 91.3.0 are vulnerable to the heap overflow described in CVE-2021-43527 when processing S/MIME messages. Thunderbird versions 91.3.0 and later will not call the vulnerable code when processing S/MIME messages that contain certificates with DER-encoded DSA or RSA-PSS signatures.

Patch / fix

  • Mozilla Thunderbird 91.3.0
  • thunderbird Debian 14, Debian 13, Debian 12 1:91.3.0-1

debian advisories DEBIAN-CVE-2021-43529

  • 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-2021-43529

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 7 91.3.0-2.el7_9
  • thunderbird RHEL 8 91.3.0-2.el8_4
  • thunderbird RHEL 8.1 EUS 91.3.0-2.el8_1
  • thunderbird RHEL 8.2 EUS 91.3.0-2.el8_2

red hat advisories RHSA-2021:4133RHSA-2021:4132RHSA-2021:4134RHSA-2021:4130

  • thunderbird Rocky Linux 8 91.3.0-2.el8_4
  • thunderbird Rocky Linux 8 91.3.0-2.el8

rocky linux advisories RLSA-2021:4130

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-2021-43529 updated cvss 9.8

thunderbird: Memory corruption when processing S/MIME messages

  • Red Hat Enterprise Linux 6 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) thunderbird 91.3.0-2.el8_4
    fixed: vendor fix RHSA-2021:4130
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird 91.3.0-2.el8_1
    fixed: vendor fix RHSA-2021:4133
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird 91.3.0-2.el8_2
    fixed: vendor fix RHSA-2021:4132
  • Red Hat Enterprise Linux Client (v. 7) thunderbird 91.3.0-2.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) thunderbird 91.3.0-2.el7_9 Red Hat Enterprise Linux Workstation (v. 7) thunderbird 91.3.0-2.el7_9
    fixed: vendor fix RHSA-2021:4134
  • Red Hat Enterprise Linux 9 thunderbird
    not affected: vulnerable code not present

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
total
Assessed
19 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 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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.