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FirefoxWeb browser · Mozilla

CVE-2026-8961

MEDIUM · 6.5 CVSS v3.1 Published 2026-05-19
Fix available
A fix is available. Upgrade to 140.11 / 140.11.0 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
Spoofing issue in the Form Autofill component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

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

A spoofing vulnerability in the Form Autofill component of Firefox, Firefox ESR, and Thunderbird allows attackers to potentially trick the browser into filling sensitive information (like credentials or personal data) into malicious or disguised form fields, leading to data being submitted to unintended destinations.

MitigationApply the vendor-supplied updates: upgrade to Firefox 151+, Firefox ESR 140.11+, Thunderbird 151+, or Thunderbird 140.11+ 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:< 140.11.0< 151.0.0
ThunderbirdApplication
Affected:< 140.11< 151.0.0

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. Check Firefox browser version
    Open Firefox, click the menu button (three horizontal lines), select Help, then select About Firefox. Note the version number displayed.
    Affected if The installed version is below 140.11.0 or falls between 140.11.0 and 151.0.0 (non-inclusive)
  2. Check Thunderbird email client version
    Open Thunderbird, click the menu button, select Help, then select About Thunderbird. Note the version number displayed.
    Affected if The installed version is below 140.11 or falls between 140.11 and 151.0.0 (non-inclusive)
  3. Verify Form Autofill is enabled in Firefox
    In Firefox address bar, type about:preferences#privacy and press Enter. Scroll to the Forms and Passwords section. Check if 'Autofill addresses' or 'Autofill credit cards' is turned on.
    Affected if Any Form Autofill feature is enabled (addresses or credit cards)
  4. Verify Form Autofill is enabled in Thunderbird
    In Thunderbird, go to Edit > Account Settings. Look for the Form Autofill or Compositing & Addressing section in each mail account settings.
    Affected if Form Autofill or address auto-completion is enabled

You are affected if you run Firefox below 140.11.0 (or between 140.11.0 and 151.0.0), or Thunderbird below 140.11 (or between 140.11 and 151.0.0), AND have any Form Autofill feature enabled.

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 140.11 / 140.11.0 / 151.0.0 or later
Fixed in 140.11140.11.0151.0.0
Interim mitigation

Apply the vendor-supplied updates: upgrade to Firefox 151+, Firefox ESR 140.11+, Thunderbird 151+, or Thunderbird 140.11+ to remediate this vulnerability.

Recommended fix High confidence

Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11 depending on product and release channel

  1. Check current Firefox or Thunderbird version via Help > About Firefox or Help > About Thunderbird
  2. Navigate to https://www.mozilla.org/en-US/firefox/releases/ or https://www.mozilla.org/en-US/thunderbird/releases/ to download the latest version
  3. Download and install Firefox 151 (or Firefox ESR 140.11 for extended support release users)
  4. For Thunderbird users, download and install Thunderbird 151 (or Thunderbird 140.11)
  5. Restart the application after installation
  6. Verify the update was successful by checking Help > About again
Caveat Major version upgrades (Firefox/Thunderbird 151) may introduce minor compatibility changes with extensions or websites

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,424.

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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-2026-8961 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