What is CVE-2026-4728?

CVE-2026-4728 is a medium-severity vulnerability in Mozilla Firefox, classified under Authentication Bypass by Spoofing. CVSS score: 6.5/10. Published 2026-03-24.

How severe is CVE-2026-4728?

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

Vulnerability in Mozilla Firefox

CVE-2026-4728

Spoofing issue in the Privacy: Anti-Tracking component. This vulnerability was fixed in Firefox 149 and Thunderbird 149.

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: 0.003 (24.4th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 24th percentile — 24.4% 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: 0.003 · change: +0.001

Affected products

Mozilla Firefox — versions 149
Mozilla Thunderbird — versions 149

Weakness classification (CWE)

CWE-290 — Authentication Bypass by Spoofing

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-20/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-23/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-4728?: CVE-2026-4728 is a medium-severity vulnerability in Mozilla Firefox, classified under Authentication Bypass by Spoofing. CVSS score: 6.5/10. Published 2026-03-24.
How severe is CVE-2026-4728?: Medium severity. CVSS v3 base score is 6.5 out of 10.