FirefoxWeb browser · Mozilla
CVE-2025-6429
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedFirefox 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceFirefox contained a URL parsing flaw where URLs specified in embed tags were incorrectly parsed and rewritten to the youtube.com domain. This allowed attackers to bypass website security checks that restrict which domains can be embedded, potentially enabling clickjacking or malicious content injection attacks.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
FirefoxWeb browser
< 128.12.0< 140.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- 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
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Firefox versionOpen Firefox, click Help in the menu bar, then select About Firefox. The version number will display in the dialog that opens. Alternatively, run 'firefox --version' from command line.Affected if The version shown is below 128.12.0 OR below 140.0 (for example, versions 129.x through 139.x are also affected)
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Confirm Firefox release channelIn Firefox, navigate to Settings > About Firefox. The page will display whether you are on Firefox, Firefox ESR, or Thunderbird, and the version.Affected if You are on Firefox (not ESR or Thunderbird) and the version falls within an affected range (< 128.12.0 or < 140.0)
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Verify patch deployment statusCheck your organization's software inventory or endpoint management system for Firefox version information across managed devices.Affected if Any managed Firefox installation reports a version below 128.12.0 or below 140.0
You are affected if any Firefox installation in your environment is version 128.11.x or lower, or any version from 129.x through 139.x.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped128.12.0140.0
Update affected installations to Firefox 140, Firefox ESR 128.12, Thunderbird 140, or Thunderbird 128.12. Organizations should verify all browser instances are patched and consider deploying updated versions enterprise-wide.
Firefox 140 / Firefox ESR 128.12 / Thunderbird 140 / Thunderbird ESR 128.12
- Upgrade Firefox to version 140 or higher
- If using Firefox ESR, upgrade to version 128.12 or higher
- Alternatively, upgrade Thunderbird to version 140 or higher, or Thunderbird ESR 128.12 or higher
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,744.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-6429 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-6429 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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