Incorrect parsing of URLs could have allowed embedding of youtube.com

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Summary

CVECVE-2025-6429
StatePUBLISHED
Assignermozilla
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-06-24 13:15:23 UTC
Updated2026-04-13 15:17:07 UTC
DescriptionFirefox 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS: 0.001190000 probability, percentile 0.308050000 (date 2026-04-15)

Problem Types: CWE-116 | CWE-116 CWE-116 Improper Encoding or Escaping of Output

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Mozilla Firefox All All All All
Application Mozilla Firefox All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mozilla Firefox unaffected 128.12 128.* rpm Not specified
CNA Mozilla Firefox unaffected 140 * rpm Not specified
CNA Mozilla Thunderbird unaffected 128.12 128.* rpm Not specified
CNA Mozilla Thunderbird unaffected 140 * rpm Not specified

References

ReferenceSourceLinkTags
www.mozilla.org/security/advisories/mfsa2025-53 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2025-51 [email protected] www.mozilla.org Vendor Advisory
www.mozilla.org/security/advisories/mfsa2025-54 [email protected] www.mozilla.org
www.mozilla.org/security/advisories/mfsa2025-55 [email protected] www.mozilla.org
bugzilla.mozilla.org/show_bug.cgi [email protected] bugzilla.mozilla.org Permissions Required
lists.debian.org/debian-lts-announce/2025/06/msg00029.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
lists.debian.org/debian-lts-announce/2025/07/msg00002.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Masato Kinugawa (en)

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