What is CVE-2020-12398?

CVE-2020-12398 is a high-severity vulnerability in Mozilla Thunderbird, classified under Cleartext Transmission of Sensitive Information. CVSS score: 7.5/10. Published 2020-07-09.

How severe is CVE-2020-12398?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Mozilla Thunderbird

CVE-2020-12398

If Thunderbird is configured to use STARTTLS for an IMAP server, and the server sends a PREAUTH response, then Thunderbird will continue with an unencrypted connection, causing email data to be sent without protection. This vulnerability affects Thunderbird < 68.9.0.

Published 2020-07-09 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.010 (60.6th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 61st percentile — 60.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.010 · newest: 0.010 · change: 0.000

Affected products

Mozilla Thunderbird — versions unspecified
Canonical Ubuntu Linux — versions 16.04, 18.04, 19.10

Weakness classification (CWE)

CWE-319 — Cleartext Transmission of Sensitive Information

References

www.mozilla.org/security/advisories/mfsa2020-22/ (Vendor Advisory)
bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking, Vendor Advisory)
usn.ubuntu.com/4421-1/ (vendor-advisory, Third Party Advisory)

Frequently asked questions

What is CVE-2020-12398?: CVE-2020-12398 is a high-severity vulnerability in Mozilla Thunderbird, classified under Cleartext Transmission of Sensitive Information. CVSS score: 7.5/10. Published 2020-07-09.
How severe is CVE-2020-12398?: High severity. CVSS v3 base score is 7.5 out of 10.