CVE-2025-6434

low-risk

Published 2025-06-24

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.

Do I need to act?

0.05% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 4.3/10 Medium

NETWORK / LOW complexity

Affected Products (1)

Firefox

Affected Vendors

Mozilla

References (3)

Permissions Required https://bugzilla.mozilla.org/show_bug.cgi?id=1955182

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

https://www.mozilla.org/security/advisories/mfsa2025-54/

/ 100

low-risk

Severity 18/34 · Moderate

Exploitability 0/34 · Minimal

Exposure 5/34 · Minimal