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6.5 Medium

CVE-2025-6429 Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in…

Description

Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an `embed` tag. This could have bypassed website security checks that restricted which domains users were allowed to embed. This vulnerability was fixed in Firefox 140, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

Affected products and versions

Product Affected versions Fixed in
Firefox 140 earliest → < 140 140
Firefox 128.12 earliest → < 128.12 128.12
Firefox ESR 128.12 earliest → < 128.12 128.12
Thunderbird 140 earliest → < 140 140
Thunderbird 128.12 earliest → < 128.12 128.12

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-2026-118026 Invalid pointer in the JavaScript: GC component 8.8 High
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