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FirefoxWeb browser · Mozilla

CVE-2026-2767

CRITICAL · 9.8 CVSS v3.1 Published 2026-02-24
Fix available
A fix is available. Upgrade to 140.8.0 / 148.0 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
Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

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

Use-after-free vulnerability in the JavaScript WebAssembly component allowing memory to be accessed after being freed, potentially enabling arbitrary code execution or memory corruption.

MitigationUpdate affected Mozilla products to Firefox 148+, Firefox ESR 140.8+, Thunderbird 148+, or Thunderbird 140.8+ to apply the patched versions.

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:< 140.8.0< 148.0
ThunderbirdApplication
Affected:< 140.8.0< 148.0

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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. Check Firefox version
    Open Firefox and navigate to Help > About Firefox, or type 'about:support' in the address bar. The version number is displayed at the top of the page.
    Affected if The displayed version is less than 140.8.0 or falls between 141.x and 147.x (less than 148.0)
  2. Check Thunderbird version
    Open Thunderbird and navigate to Help > About Thunderbird. The version number is displayed in the dialog that opens.
    Affected if The displayed version is less than 140.8.0 or falls between 141.x and 147.x (less than 148.0)
  3. Confirm WebAssembly usage in Firefox
    WebAssembly is enabled by default in Firefox. To verify, go to about:config and search for 'javascript.options.wasm'. A value of 'true' indicates WebAssembly is enabled.
    Affected if WebAssembly is enabled and the Firefox version is vulnerable per step 1. If WebAssembly is disabled, the exploit surface is reduced but the install is still considered outdated.
  4. Confirm WebAssembly usage in Thunderbird
    Thunderbird also includes JavaScript engine components with WebAssembly support. Check about:config for 'javascript.options.wasm' set to 'true'.
    Affected if WebAssembly is enabled and the Thunderbird version is vulnerable per step 2.

Your environment is affected if either Firefox or Thunderbird is installed with a version below 140.8.0 or in the range 141.x-147.x (below 148.0), regardless of WebAssembly being enabled or disabled.

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 140.8.0 / 148.0 or later
Fixed in 140.8.0148.0
Interim mitigation

Update affected Mozilla products to Firefox 148+, Firefox ESR 140.8+, Thunderbird 148+, or Thunderbird 140.8+ to apply the patched versions.

Recommended fix High confidence

Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8

  1. Check the currently installed version of Firefox or Thunderbird by navigating to the application menu and selecting 'About Firefox' or 'About Thunderbird'
  2. For Firefox users: Download and install Firefox 148 (or Firefox ESR 140.8 for organizations using the Extended Support Release)
  3. For Thunderbird users: Download and install Thunderbird 148 (or Thunderbird 140.8 for organizations using the Extended Support Release)
  4. Restart the application after upgrade
  5. Verify the upgrade was successful by checking the version in 'About Firefox' or 'About Thunderbird' confirms the installed version matches the fixed release

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.

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-2026-2767 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