CVE-2020-12398
Mozilla: Security downgrade with IMAP STARTTLS leads to information leakage
Severity
ImportantRed Hat Product Security
CVSS 3.0
Review impact separately from score.
Published · June 2, 2020
Updated · November 22, 2025
Description
The Mozilla Foundation Security Advisory describes this flaw as:
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.
CVSS score applicability
The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.
Mitigation
No mitigation is specified in collected source.
CVSS / CWE
CVSS 3.0 · 7.5CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor