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.

Published 2026-03-24 · last modified 2026-06-17.

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.

EPSS exploit prediction

EPSS: 0.004 (26.9th percentile), scored 2026-10-05.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 26.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002

Affected products

Mozilla Thunderbird — versions 140.9, 149

Weakness classification (CWE)

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

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-23/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-24/ (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.