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4.0 Medium

CVE-2025-0239 When using Alt-Svc, ALPN did not properly validate certificates when the original server is redirecting to an insecure…

Description

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.

Affected products and versions

Product Affected versions Fixed in
Firefox 134 earliest → < 134 134
Firefox 128.6 earliest → < 128.6 128.6
Firefox ESR 128.6 earliest → < 128.6 128.6
Thunderbird 134 earliest → < 134 134
Thunderbird 128.6 earliest → < 128.6 128.6

Other CVEs of Firefox

The 2221 CVEs of Firefox →
CVE-2026-120572 Incorrect boundary conditions in the Layout: Block and Inline component 8.8 High CVE-2026-118027 Frame poisoning in the Layout component 9.1 Critical CVE-2026-118025 Other issue in the SVG component 8.8 High CVE-2026-118024 Use-after-free in the Graphics: Text component 8.8 High
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