What’s Vulnerable › Vulnerabilities

CVE-2025-6429: Incorrect parsing of URLs could have allowed embedding of youtube.com

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-06-24 · updated 2026-09-30
• Weakness: CWE-116

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: before 128.12.0; before 140.0 — fixed in 128.12.0, 140.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 128.12.0, 140.0. Check the vendor advisory for mitigations.

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/2025/06/msg00029.html
• https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html

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