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FirefoxWeb browser · Mozilla

CVE-2026-6765

MEDIUM · 5.3 CVSS v3.1 Published 2026-04-21
Fix available
A fix is available. Upgrade to 140.10.0 / 150.0 or later.
See remediation →
62/100
Remediation priority · Elevated
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
Information disclosure in the Form Autofill component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

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

An information disclosure vulnerability exists in the Form Autofill component of Firefox, Firefox ESR, and Thunderbird. This flaw allows sensitive information entered into web forms to be potentially exposed. The vulnerability was addressed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

MitigationUpdate affected installations to Firefox 150, Firefox ESR 140.10, Thunderbird 150, Thunderbird 140.10 or later versions. Organizations should inventory all deployed browser installations and ensure consistent patching.

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:< 140.10.0< 150.0
ThunderbirdApplication
Affected:< 140.10.0

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
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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. Identify installed Mozilla product
    Check if Firefox, Firefox ESR, or Thunderbird is installed. In the application, go to Help > About to see the product name and version. Firefox ESR will say 'Firefox ESR' in the version string.
    Affected if Product is Firefox, Firefox ESR, or Thunderbird with a version below the fixed releases
  2. Check Firefox version
    In Firefox, navigate to about:support or go to Help > About Firefox. Note the version number displayed (e.g., 140.0, 139.0).
    Affected if Version is below 150.0 (for regular Firefox)
  3. Check Firefox ESR version
    In Firefox ESR, navigate to about:support or go to Help > About Firefox. The version will display as 'Firefox ESR 140.x' or similar.
    Affected if Version is below 140.10.0 (for Firefox ESR)
  4. Check Thunderbird version
    In Thunderbird, go to Help > About Thunderbird. Note the version number displayed.
    Affected if Version is below 140.10.0 (for Thunderbird)
  5. Verify Form Autofill is enabled
    In Firefox or Thunderbird, go to about:preferences#privacy and scroll to the Form Autofill section. Alternatively, search about:config for 'formfill' or 'autofill' preferences to confirm the feature is active.
    Affected if Form Autofill is enabled and the version is vulnerable as shown in steps 2-4

A user is affected if they have Firefox below 150.0, Firefox ESR below 140.10.0, or Thunderbird below 140.10.0 with Form Autofill 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 140.10.0 / 150.0 or later
Fixed in 140.10.0150.0
Interim mitigation

Update affected installations to Firefox 150, Firefox ESR 140.10, Thunderbird 150, Thunderbird 140.10 or later versions. Organizations should inventory all deployed browser installations and ensure consistent patching.

Recommended fix High confidence

Firefox 150+ / Firefox ESR 140.10+ / Thunderbird 140.10+

  1. 1. Check the currently installed Firefox version by navigating to about:support in the browser address bar
  2. 2. Check the currently installed Thunderbird version by navigating to Help > About Thunderbird
  3. 3. For Firefox users: Download and install Firefox 150.0 or later from www.mozilla.org/firefox/
  4. 4. For Firefox ESR users: Download and install Firefox ESR 140.10 or later from www.mozilla.org/firefoxfox/esr/
  5. 5. For Thunderbird users: Download and install Thunderbird 140.10 or later from www.mozilla.org/thunderbird/
  6. 6. After installation, verify the version by checking about:support (Firefox) or Help > About Thunderbird to confirm the fix is applied
Caveat Standard minor version upgrade; no major breaking changes expected for this security patch

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
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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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-2026-6765 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