What is CVE-2025-4086?

CVE-2025-4086 is a medium-severity vulnerability in Mozilla Firefox, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2025-04-29.

How severe is CVE-2025-4086?

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

Vulnerability in Mozilla Firefox

CVE-2025-4086

A specially crafted filename containing a large number of encoded newline characters could obscure the file's extension when displayed in the download dialog. *This bug only affects Thunderbird for Android. Other versions of Thunderbird are unaffected.*. This vulnerability was fixed in Firefox 138 and Thunderbird 138.

Published 2025-04-29 · 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:N/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (19.4th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 19th percentile — 19.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.000

Affected products

Mozilla Firefox — versions 138
Mozilla Thunderbird — versions 138

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/mfsa2025-28/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2025-31/ (Vendor Advisory)

Frequently asked questions

What is CVE-2025-4086?: CVE-2025-4086 is a medium-severity vulnerability in Mozilla Firefox, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2025-04-29.
How severe is CVE-2025-4086?: Medium severity. CVSS v3 base score is 6.5 out of 10.