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
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Mozilla Firefox
128.12 to ≤ 128.*unaffected140 to ≤ *unaffected
Mozilla Thunderbird
128.12 to ≤ 128.*unaffected140 to ≤ *unaffected
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1970658 ↗
- https://www.mozilla.org/security/advisories/mfsa2025-51/ ↗
- https://www.mozilla.org/security/advisories/mfsa2025-53/ ↗
- https://www.mozilla.org/security/advisories/mfsa2025-54/ ↗
- https://www.mozilla.org/security/advisories/mfsa2025-55/ ↗
- https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html ↗
- https://lists.debian.org/debian-lts-announce/2025/06/msg00029.html ↗