What is CVE-2026-16403?

CVE-2026-16403 is a medium-severity vulnerability in Mozilla Firefox, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2026-07-21.

How severe is CVE-2026-16403?

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

Vulnerability in Mozilla Firefox

CVE-2026-16403

Spoofing issue in the Address Bar component. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

EPSS: 0.002 (9.6th 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 Firefox — versions 153
Mozilla Thunderbird — versions 153

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-2026-16403?: CVE-2026-16403 is a medium-severity vulnerability in Mozilla Firefox, classified under User Interface (UI) Misrepresentation of Critical Information. CVSS score: 6.5/10. Published 2026-07-21.
How severe is CVE-2026-16403?: Medium severity. CVSS v3 base score is 6.5 out of 10.