CVE-2025-0239

low-risk

Published 2025-01-07

When using Alt-Svc, ALPN did not properly validate certificates when the original server is redirecting to an insecure site. This vulnerability was fixed in Firefox 134, Firefox ESR 128.6, Thunderbird 134, and Thunderbird 128.6.

Do I need to act?

0.03% 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 4.0/10 Medium

LOCAL / LOW complexity

Affected Products (3)

Firefox

Thunderbird

Affected Vendors

Mozilla

References (6)

Issue Tracking https://bugzilla.mozilla.org/show_bug.cgi?id=1929156

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2025-01/

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2025-02/

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2025-04/

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2025-05/

https://lists.debian.org/debian-lts-announce/2025/01/msg00004.html

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low-risk

Severity 14/34 · Moderate

Exploitability 0/34 · Minimal

Exposure 9/34 · Low