CVE-2025-6434: firefox — Fix

Description

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.

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CVSS v3.1 Score

4.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Weakness Type (CWE)

CWE-1021 CWE-1021

Affected Products

Vendor	Product	Versions
mozilla	firefox	< 140.0

References

Advisories & Patches

https://www.mozilla.org/security/advisories/mfsa2025-51/

Other References

https://bugzilla.mozilla.org/show_bug.cgi?id=1955182 https://www.mozilla.org/security/advisories/mfsa2025-54/

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 4.3 (MEDIUM).

How severe is CVE-2025-6434? +

CVE-2025-6434 has a CVSS v3.1 score of 4.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-6434? +

CVE-2025-6434 affects products from mozilla, specifically: firefox. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-6434? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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