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Vulnerabilities

Vulnerability · CVE-2025-6429

Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an tag.

Published Jun 24, 2025 · catalog updated Apr 13, 2026 · Firefox could have incorrectly

Check this week

CVE-2025-6429 is not in CISA KEV. FIRST estimates a 36.00% chance of exploitation in the next 30 days. Check whether you run Firefox could have incorrectly.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Firefox could have incorrectly).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
36.00%
Remediation
Advisory link
Affected products
vendor mozilla

Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an 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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor mozillaversion unspecified

How to fix CVE-2025-6429

  • Recommended remediation

    A patch or advisory reference is linked. Open the original publisher for availability by product version.

  • Official advisories

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2025-6429 is not in CISA KEV. FIRST estimates a 36.00% chance of exploitation in the next 30 days. Check whether you run Firefox could have incorrectly.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 36.00%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jun 24, 2025 · EUVD

    Detected

    Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an 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.

  2. Apr 13, 2026 · EUVD

    Updated

    Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an 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.

Sources

  • EUVDVulnerability recordEUVD-2025-21378

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

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Apr 13, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.