---
id: CVE-2025-6429
title: >-
  Firefox could have incorrectly parsed a URL and rewritten it to the
  youtube.com domain when parsing the URL specified in an `embed` tag
summary: >-
  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 t…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N'
cwe:
  - CWE-116
vendor: mozilla
product: firefox
affected:
  - firefox < 128.12.0
  - firefox < 140.0
patched:
  - firefox 140.0
published: '2025-06-24'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6429'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1970658'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-51/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-53/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-54/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-55/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/06/msg00029.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/07/msg00002.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00355
epssPercentile: 0.26824
ingestedAt: '2026-09-30T18:17:24.444Z'
---

## Overview

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

- `firefox < 128.12.0`
- `firefox < 140.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.0`