What is CVE-2025-6434?

CVE-2025-6434 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Rendered UI Layers or Frames (Clickjacking). CVSS score: 4.3/10. Published 2025-06-24.

How severe is CVE-2025-6434?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Mozilla Firefox

CVE-2025-6434

The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an attacker to trick a user into granting an exception and loading a webpage over HTTP. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

EPSS: 0.002 (13.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N.

Affected products

Mozilla Firefox — versions 140
Mozilla Thunderbird — versions 140

Weakness classification (CWE)

CWE-1021 — Improper Restriction of Rendered UI Layers or Frames (Clickjacking)

References

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

Frequently asked questions

What is CVE-2025-6434?: CVE-2025-6434 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Rendered UI Layers or Frames (Clickjacking). CVSS score: 4.3/10. Published 2025-06-24.
How severe is CVE-2025-6434?: Medium severity. CVSS v3 base score is 4.3 out of 10.