What is CVE-2026-3889?

CVE-2026-3889 is a medium-severity vulnerability in Mozilla Thunderbird, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2026-03-24.

How severe is CVE-2026-3889?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Mozilla Thunderbird

CVE-2026-3889

Spoofing issue in Thunderbird. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9.

EPSS: 0.002 (10.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N.

Affected products

Mozilla Thunderbird — versions 140.9, 149

Weakness classification (CWE)

CWE-451 — User Interface (UI) Misrepresentation of Critical Information

References

security@mozilla.org (Permissions Required)
security@mozilla.org (Vendor Advisory)
security@mozilla.org (Vendor Advisory)

Frequently asked questions

What is CVE-2026-3889?: CVE-2026-3889 is a medium-severity vulnerability in Mozilla Thunderbird, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2026-03-24.
How severe is CVE-2026-3889?: Medium severity. CVSS v3 base score is 6.5 out of 10.