#VU102425 Improper Certificate Validation in Mozilla Firefox and Firefox ESR - CVE-2025-0239

Vulnerability identifier: #VU102425

Vulnerability risk: Medium

CVSSv4.0: 1.2 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2025-0239

CWE-ID: CWE-295

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Mozilla Firefox
Client/Desktop applications / Web browsers
Firefox ESR
Client/Desktop applications / Web browsers

Vendor: Mozilla

Description

The vulnerability allows a remote attacker to perform MitM attack.

The vulnerability exists due to Alt-Svc ALPN does not properly validate certificates when the original server is redirecting to an insecure site. A remote attacker can perform MitM attack.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Mozilla Firefox: 128.0 - 133.0.3

Firefox ESR: 128.0 - 128.5.2

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External links
https://bugzilla.mozilla.org/show_bug.cgi?id=1929156
https://www.mozilla.org/security/advisories/mfsa2025-01/
https://www.mozilla.org/security/advisories/mfsa2025-02/

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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.