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Fencer Vulns
medium 5.9

CVE-2021-38502 json

Thunderbird ignored the configuration to require STARTTLS security for an SMTP connection.

published 2021-11-03 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-24954

cvss
5.9
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 65%
public exploits
0
none known

Summary

Thunderbird ignored the configuration to require STARTTLS security for an SMTP connection. A MITM could perform a downgrade attack to intercept transmitted messages, or could take control of the authenticated session to execute SMTP commands chosen by the MITM. If an unprotected authentication method was configured, the MITM could obtain the authentication credentials, too. This vulnerability affects Thunderbird < 91.2.

Patch / fix

  • Mozilla Thunderbird 91.2
  • thunderbird Debian 14, Debian 13, Debian 12 1:91.2.1-1

debian advisories DEBIAN-CVE-2021-38502

  • 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
  • thunderbird Ubuntu 22.04 LTS 1:91.3.1+build1-0ubuntu1

ubuntu advisories UBUNTU-CVE-2021-38502

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 91.2.0-1.el7_9
  • thunderbird RHEL 8 91.2.0-1.el8_4
  • thunderbird RHEL 8.2 EUS 91.2.0-1.el8_2
  • thunderbird RHEL 8.1 EUS 91.2.0-1.el8_1

red hat advisories RHSA-2021:3839RHSA-2021:3841RHSA-2021:3838RHSA-2021:3840

  • 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 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-2021:1635-1openSUSE-SU-2021:4150-1

  • thunderbird Rocky Linux 8 91.2.0-1.el8_4

rocky linux advisories RLSA-2021:3838

  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 91.3.2-r0

alpine advisories ALPINE-CVE-2021-38502

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 91.2.0-1

arch linux advisories AVG-2459

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-2021-38502 updated cvss 7.5

Mozilla: Downgrade attack on SMTP STARTTLS connections

  • Red Hat Enterprise Linux 6 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) thunderbird 91.2.0-1.el8_4
    fixed: vendor fix RHSA-2021:3838
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird 91.2.0-1.el8_1
    fixed: vendor fix RHSA-2021:3840
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird 91.2.0-1.el8_2
    fixed: vendor fix RHSA-2021:3839
  • Red Hat Enterprise Linux Client (v. 7) thunderbird 91.2.0-1.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) thunderbird 91.2.0-1.el7_9 Red Hat Enterprise Linux Workstation (v. 7) thunderbird 91.2.0-1.el7_9
    fixed: vendor fix RHSA-2021:3841

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

1.10% chance of exploitation in the next 30 days, higher than 65% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:P/I:N/A:N

Affected products

  • Mozilla Thunderbird

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.