#VU111895 Protection Mechanism Failure in Mozilla Firefox and Firefox for Android - CVE-2025-6434

Vulnerability identifier: #VU111895

Vulnerability risk: Low

CVSSv4.0: 0.5 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2025-6434

CWE-ID: CWE-693

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Mozilla Firefox
Client/Desktop applications / Web browsers
Firefox for Android
Mobile applications / Apps for mobile phones

Vendor: Mozilla

Description

The vulnerability allows a remote attacker to bypass implemented security restrictions.

The vulnerability exists due to 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.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Mozilla Firefox: 130.0 - 139.0.4

Firefox for Android: 130.0 - 139.0.3

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External links
https://www.mozilla.org/en-US/security/advisories/mfsa2025-51/
https://bugzilla.mozilla.org/show_bug.cgi?id=1955182

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.