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FirefoxWeb browser · Mozilla

CVE-2025-3029

HIGH · 7.3 CVSS v3.1 Published 2025-04-01
Fix available
A fix is available. Upgrade to 128.9.0 / 137.0 or later.
See remediation →
82/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
A crafted URL containing specific Unicode characters could have hidden the true origin of the page, resulting in a potential spoofing attack. This vulnerability was fixed in Firefox 137, Firefox ESR 128.9, Thunderbird 137, and Thunderbird 128.9.

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 confidence

A crafted URL containing specific Unicode characters could hide the true origin of the page, resulting in a URL spoofing vulnerability in Firefox and Thunderbird. This allows attackers to display a deceptive origin in the address bar while actually navigating to a different site.

MitigationUpdate to Firefox 137, Firefox ESR 128.9, Thunderbird 137, Thunderbird 128.9 or later versions to apply the security fix.

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
Affected:< 128.9.0< 137.0
ThunderbirdApplication
Affected:< 128.9.0>= 129.0, < 137.0

CVSS 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
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

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

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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify the installed Mozilla product
    Open the application and navigate to Help > About (Firefox) or Help > About Thunderbird to see which product is installed.
    Affected if Product is Firefox or Thunderbird
  2. Check Firefox version
    In Firefox, go to Help > About Firefox. Note the version number displayed (e.g., 136.0.1, 128.8.0, etc.).
    Affected if Firefox version is less than 128.9.0 OR less than 137.0 (any version before 137.0)
  3. Check Thunderbird version
    In Thunderbird, go to Help > About Thunderbird. Note the version number displayed.
    Affected if Thunderbird version is less than 128.9.0 OR between 129.0 and 136.x (any version before 137.0 but 128.9.0 or higher)
  4. Verify attack surface
    Determine if users could encounter untrusted URLs, particularly from external sources, emails, or websites that might contain crafted Unicode characters in links.
    Affected if Users can access external URLs or view email content with embedded links

If the installed Firefox or Thunderbird version is lower than 137.0 (specifically below 128.9.0 or between 129.0-136.x), the environment is vulnerable to URL spoofing via Unicode characters.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 128.9.0 / 137.0 or later
Fixed in 128.9.0137.0
Interim mitigation

Update to Firefox 137, Firefox ESR 128.9, Thunderbird 137, Thunderbird 128.9 or later versions to apply the security fix.

Recommended fix High confidence

Firefox 137 (stable) or Firefox ESR 128.9; Thunderbird 137 or Thunderbird 128.9

  1. 1. Back up any critical data (bookmarks, passwords, email data for Thunderbird) before upgrading
  2. 2. Close all instances of Firefox or Thunderbird
  3. 3. For Firefox: Navigate to Mozilla's official download page (www.mozilla.org) and download Firefox 137 (stable) or Firefox ESR 128.9 for enterprise/long-term support needs
  4. 4. For Thunderbird: Navigate to Mozilla's official download page (www.mozilla.org) and download Thunderbird 137 or Thunderbird 128.9
  5. 5. Run the installer and follow the prompts to complete the upgrade
  6. 6. Alternatively, use the application's built-in update mechanism: Help > About Firefox/Thunderbird > Check for Updates
  7. 7. After upgrading, verify the version by checking Help > About to confirm the installed version
Caveat Minor: This is a security patch release with no major breaking changes expected; users on very old configurations should review add-on compatibility

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
3.0 hours of engineering $750
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-3029 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data