CVE-2025-6434 HTTPS-Only exception screen lacked anti-clickjacking delay

What is CVE-2025-6434?

CVE-2025-6434 is a medium-severity vulnerability in Mozilla Firefox, published on 24 Jun 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official 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.

Weakness: CWE-1021

Which versions are affected by CVE-2025-6434?

It affects 1 product.

Products include Mozilla Firefox.

How do I fix CVE-2025-6434?

Upgrade to a fixed version.

Is CVE-2025-6434 being exploited?

There is no known exploitation of CVE-2025-6434 in the wild and no public exploit code.

Other vulnerabilities in Mozilla Firefox

• CVE-2019-11708 Mozilla Firefox and Thunderbird Sandbox Escape Exploited Critical 10.0
• CVE-2010-3765 Mozilla Multiple Products Remote Code Execution Exploited Critical 9.8
• CVE-2022-26486 Mozilla Firefox Use-After-Free Exploited Critical 9.6
• CVE-2022-26485 Mozilla Firefox Use-After-Free Exploited High 8.8
• CVE-2019-11707 Mozilla Firefox and Thunderbird Type Confusion Exploited High 8.8

All Mozilla Firefox vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-87mm-rg9r-h8wm, UBUNTU-CVE-2025-6434.