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
mozilla: firefox
References7
- www.mozilla.org/security/advisories/mfsa2025-51/ Vendor Advisory
- www.mozilla.org/security/advisories/mfsa2025-53/ Vendor Advisory
- bugzilla.mozilla.org/show_bug.cgi?id=1970658 Permissions Required
- www.mozilla.org/security/advisories/mfsa2025-54/
- www.mozilla.org/security/advisories/mfsa2025-55/
- lists.debian.org/debian-lts-announce/2025/06/msg00029.html
- lists.debian.org/debian-lts-announce/2025/07/msg00002.html
Metrics
- CVSS 3.1
-
6.5
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N - EPSS — exploit probability
- 0% percentile: 29 · as of 7 November 2026
- CWE
- CWE-116
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