cve/2025/CVE-2025-0239.md

### [CVE-2025-0239](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-0239)
![](https://img.shields.io/static/v1?label=Product&message=Firefox%20ESR&color=blue)
![](https://img.shields.io/static/v1?label=Product&message=Firefox&color=blue)
![](https://img.shields.io/static/v1?label=Product&message=Thunderbird&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=unspecified%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Vulnerability&message=Alt-Svc%20ALPN%20validation%20failure%20when%20redirected&color=brightgreen)

### Description

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

### POC

#### Reference
- https://bugzilla.mozilla.org/show_bug.cgi?id=1929156

#### Github
No PoCs found on GitHub currently.