CVE-2021-38502

Name: CVE-2021-38502
Creator: NVD / NIST
Published: 2021-11-03T01:15:07.657+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.9/10EPSS 1.07%

Last modified Jun 17, 2026

CVE-2021-38502 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. 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. EPSS estimates a 1.07% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Probability

1.07%

60.5th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Mozilla	Thunderbird	< 91.2
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0
Debian	Debian Linux	11.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1733366Issue Tracking, Permissions Required, Vendor Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.htmlMailing List, Third Party Advisory
https://www.debian.org/security/2022/dsa-5034Issue Tracking, Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-47/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1733366Issue Tracking, Permissions Required, Vendor Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.htmlMailing List, Third Party Advisory
https://www.debian.org/security/2022/dsa-5034Issue Tracking, Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-47/Vendor Advisory

Timeline

Published: Nov 3, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-38502?

How severe is CVE-2021-38502?

CVE-2021-38502 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 1.07% probability of exploitation in the next 30 days.

How do I fix CVE-2021-38502?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-38502?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST