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FirefoxWeb browser · Mozilla

CVE-2026-4688

CRITICAL · 10.0 CVSS v3.1 Published 2026-03-24
Fix available
A fix is available. Upgrade to 140.9.0 / 149.0 or later.
See remediation →
100/100
Remediation priority · Urgent
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
Sandbox escape due to use-after-free in the Disability Access APIs component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

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 · moderate confidence

Use-after-free vulnerability in the Disability Access APIs component allows a malicious webpage to escape the browser sandbox and execute code outside the restricted environment. This is a critical memory corruption issue affecting Firefox and Thunderbird.

MitigationUpdate to Firefox 149, Firefox ESR 140.9, Thunderbird 149, Thunderbird 140.9 or later to remediate the 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:< 140.9.0< 149.0

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
Changed
Confidentiality
High
Integrity
High
Availability
High

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

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
    Determine whether Firefox or Thunderbird is installed on the system
    Affected if Either Firefox or Thunderbird is present
  2. Check Firefox version
    In Firefox, go to Menu > Help > About Firefox, or enter 'about:support' in the address bar to view the version under 'Application Basics'
    Affected if Version is below 140.9.0 or between 141.0 and 148.x inclusive (versions 149.0 and above are fixed)
  3. Check Thunderbird version
    In Thunderbird, go to Menu > Help > About Thunderbird to view the version number
    Affected if Version is below 140.9.0 or between 141.0 and 148.x inclusive (versions 149.0 and above are fixed)
  4. Verify if Disability Access APIs are enabled
    In Firefox, enter 'about:config' in the address bar, search for 'accessibility.enabled', and check its value. In Thunderbird, the accessibility settings are typically managed through the system-level accessibility API settings.
    Affected if Accessibility features are enabled (the vulnerability exists in the Disability Access APIs component)

A user is affected if they have Firefox or Thunderbird version below 140.9.0 or between 141.0-148.x AND have accessibility features 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 140.9.0 / 149.0 or later
Fixed in 140.9.0149.0
Interim mitigation

Update to Firefox 149, Firefox ESR 140.9, Thunderbird 149, Thunderbird 140.9 or later to remediate the vulnerability.

Recommended fix High confidence

Firefox 149 (or Firefox ESR 140.9 for ESR users)

  1. 1. Back up important data (bookmarks, passwords, history) by going to Menu > Help > More Troubleshooting Information > Profile Folder > Open Folder, then copy the profile folder to a safe location
  2. 2. Open Firefox and navigate to Menu > Help > About Firefox to check current version
  3. 3. Download Firefox 149 (or Firefox ESR 140.9 for enterprise/ESR users) from the official Mozilla website (www.mozilla.org)
  4. 4. Close all Firefox instances completely
  5. 5. Run the installer for the downloaded Firefox version
  6. 6. After installation, verify the fix by checking Menu > Help > About Firefox shows version 149 or ESR 140.9
  7. 7. Ensure automatic updates are enabled via Menu > Settings > General > Firefox Updates > Check for updates
Caveat Minimal risk - this is a security patch upgrade with no major feature changes expected

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

Fix this in Firefox Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.

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-2026-4688 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