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FirefoxWeb browser · Mozilla

CVE-2025-11712

MEDIUM · 6.1 CVSS v3.1 Published 2025-10-14
Fix available
A fix is available. Upgrade to 140.4.0 / 144.0 or later.
See remediation →
68/100
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
A malicious page could have used the type attribute of an OBJECT tag to override the default browser behavior when encountering a web resource served without a content-type. This could have contributed to an XSS on a site that unsafely serves files without a content-type header. This vulnerability was fixed in Firefox 144, Firefox ESR 140.4, Thunderbird 144, and Thunderbird 140.4.

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

In affected Mozilla products (Firefox 144 and earlier, Firefox ESR 140.4 and earlier, Thunderbird 144 and earlier, Thunderbird 140.4 and earlier), the type attribute of an OBJECT tag could override default browser behavior when processing web resources served without a Content-Type header. This allowed a malicious page to influence how the browser interpreted content, potentially leading to XSS on websites that incorrectly serve files without Content-Type headers.

MitigationUpdate affected Mozilla products to version 144 (Firefox/Thunderbird) or 140.4 (Firefox ESR/Thunderbird). Website operators should ensure all served resources include proper Content-Type headers to prevent this attack vector.

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:< 140.4.0< 144.0
ThunderbirdApplication
Affected:< 140.4.0>= 141.0, < 144.0

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
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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. Check Firefox version on the system
    On Windows, check 'C:\Program Files\Mozilla Firefox\application.ini' for version or go to Help > About Firefox. On Linux, run 'firefox --version' or check '/usr/lib/firefox/browser/application.ini'. On macOS, run 'firefox --version' or check the app bundle info.
    Affected if The installed Firefox version is less than 144.0 (including any version below 140.4.0)
  2. Check Thunderbird version on the system
    On Windows, check 'C:\Program Files\Mozilla Thunderbird\application.ini' for version or go to Help > About Thunderbird. On Linux, run 'thunderbird --version' or check '/usr/lib/thunderbird/application.ini'. On macOS, run 'thunderbird --version' or check the app bundle info.
    Affected if The installed Thunderbird version is less than 140.4.0, OR is 141.x, 142.x, or 143.x (any version from 141.0 up to but not including 144.0)
  3. Confirm presence of affected software
    Search the system for Firefox or Thunderbird executables. On Windows, check Program Files directories. On Linux, check common package management outputs like 'dpkg -l' or 'rpm -qa' for firefox or thunderbird packages.
    Affected if Any version of Firefox or Thunderbird is installed that matches the affected version ranges from steps 1 or 2

A user is affected if they have Mozilla Firefox below version 144.0 or Mozilla Thunderbird below version 140.4.0, or Thunderbird versions 141.x through 143.x installed on their system.

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 140.4.0 / 144.0 or later
Fixed in 140.4.0144.0
Interim mitigation

Update affected Mozilla products to version 144 (Firefox/Thunderbird) or 140.4 (Firefox ESR/Thunderbird). Website operators should ensure all served resources include proper Content-Type headers to prevent this attack vector.

Recommended fix High confidence

Firefox 144 or Firefox ESR 140.4; Thunderbird 144 or Thunderbird 140.4

  1. 1. Open the Firefox or Thunderbird application
  2. 2. Navigate to the Help menu (or on macOS, Firefox/Thunderbird menu)
  3. 3. Select 'About Firefox' or 'About Thunderbird'
  4. 4. The application will check for updates and download the latest version
  5. 5. Click 'Update' when prompted to install the update
  6. 6. Restart the application to complete the installation

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

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-2025-11712 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