#VU111894 Improperly implemented security check for standard in Mozilla Firefox and Firefox for Android - CVE-2025-6433

Vulnerability identifier: #VU111894

Vulnerability risk: Low

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

CVE-ID: CVE-2025-6433

CWE-ID: CWE-358

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 gain access to sensitive information.

The vulnerability exists due to an error when handling invalid TLS certificates. If a user visited a webpage with an invalid TLS certificate, and granted an exception, the webpage was able to provide a WebAuthn challenge that the user would be prompted to complete. This is in violation of the WebAuthN spec which requires "a secure transport established without errors".

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

---

External links
https://www.mozilla.org/en-US/security/advisories/mfsa2025-51/
https://bugzilla.mozilla.org/show_bug.cgi?id=1954033

---

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.