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FirefoxWeb browser · Mozilla

CVE-2025-23109

MEDIUM · 6.5 CVSS v3.1 Published 2025-01-11
Fix available
A fix is available. Upgrade to 134.0 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

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
Long hostnames in URLs could be leveraged to obscure the actual host of the website or spoof the website address. This vulnerability was fixed in Firefox for iOS 134.

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 · moderate confidence

Firefox for iOS had a vulnerability where excessively long hostnames in URLs could be used to obscure the true host of a website or spoof addresses, potentially leading users to believe they are visiting a different site than they actually are. This is a URL display/parsing issue in the browser's address bar rendering.

MitigationUpdate Firefox for iOS to version 134 or later to remediate this vulnerability.

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:< 134.0

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
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 checks

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

  1. Verify Firefox for iOS is installed
    Open the iOS Settings app, scroll to the installed apps list, and confirm Firefox appears in the list of applications.
    Affected if Firefox for iOS is not present on the device, then the vulnerability does not apply.
  2. Locate the installed version of Firefox for iOS
    Open the App Store app, search for Firefox, or go to your purchased apps list. The version number is displayed on the app's store page. Alternatively, if Firefox is already installed, open it, go to Settings > Help > About Firefox, which displays the version number.
    Affected if Unable to determine the version number from the App Store or within the app.
  3. Compare your version against the affected range
    Review the version number obtained from the previous step. The affected range is any version prior to 134.0 (for example: 133.5, 133.0, 132.x, etc.).
    Affected if The installed version is a release prior to 134.0 (for example 133.5, 132.3, or any 133.x or 132.x version), indicating the address bar may display excessively long hostnames in a way that could obscure the true host.
  4. Test URL display with long hostnames (optional verification)
    Navigate to a URL with an unusually long hostname (for example, a URL where the domain portion exceeds 60+ characters). Observe whether the address bar truncates the display in a way that makes it difficult to identify the actual domain being visited.
    Affected if The address bar shows an ambiguous or truncated view of a long hostname that makes it unclear what the true destination domain is.

A user is affected if Firefox for iOS is installed and the version is below 134.0, as this version range contains the flawed address bar hostname rendering logic.

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 134.0 or later
Fixed in 134.0
Interim mitigation

Update Firefox for iOS to version 134 or later to remediate this vulnerability.

Recommended fix High confidence

Firefox 134.0 or later

  1. Check the current Firefox version by navigating to about:support or checking the application menu
  2. Download and install Firefox version 134.0 or later from the official Mozilla website or your device's app store
  3. After installation, verify the fix by navigating to about:support to confirm the Firefox version is 134.0 or higher
  4. Test that long hostnames in URLs are properly displayed and validated in the address bar

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
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Scan for this in your stack

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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-2025-23109 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