CVE-2021-29969

Name: CVE-2021-29969
Creator: NVD / NIST
Published: 2021-08-05T20:15:08.5+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.9/10EPSS 1.20%

Last modified Jun 17, 2026

CVE-2021-29969 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. EPSS estimates a 1.20% chance of exploitation in the next 30 days.

Description

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

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

1.20%

64.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-552

Affected Software

Vendor	Product	Versions
Mozilla	Thunderbird	< 78.12

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1682370Issue Tracking, Permissions Required, Vendor Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-30/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1682370Issue Tracking, Permissions Required, Vendor Advisory
https://security.gentoo.org/glsa/202208-14Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-30/Vendor Advisory

Timeline

Published: Aug 5, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29969?

How severe is CVE-2021-29969?

CVE-2021-29969 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 1.20% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29969?

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-2021-29969?

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

Scan your code now

Source: NVD / NIST