dbcve.org
FirefoxWeb browser · Mozilla

CVE-2026-2765

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 Engine 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

A use-after-free vulnerability in the Mozilla JavaScript Engine allows memory to be accessed after being freed, potentially enabling arbitrary code execution or crashes. This memory safety flaw in the browser's JavaScript processing could be exploited via malicious web content.

MitigationUpdate affected Mozilla products (Firefox, Firefox ESR, Thunderbird) to version 148 or 140.8 (ESR) respectively, or later. Deploy through enterprise patch management systems and verify successful installation.

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 if Firefox is installed
    Open Firefox and navigate to Menu > Help > About Firefox, or run 'firefox --version' from command line. On Windows, check the version in the application's properties or registry.
    Affected if Firefox version is below 140.8.0 or between 140.8.0 and 147.x (inclusive)
  2. Check if Thunderbird is installed
    Open Thunderbird and navigate to Menu > Help > About Thunderbird, or run 'thunderbird --version' from command line. On Windows, check the version in the application's properties or registry.
    Affected if Thunderbird version is below 140.8.0 or between 140.8.0 and 147.x (inclusive)
  3. Identify installed product versions precisely
    Compare the exact version number shown in the About dialog or command output against the affected ranges: any version < 140.8.0 OR any version from 140.8.0 through 147.x is vulnerable. Versions 140.8.0 and 148.0 or higher are patched.
    Affected if Installed version falls within the vulnerable ranges

You are affected if either Firefox or Thunderbird is installed and its version is below 140.8.0 or between 140.8.0 and 147.x inclusive.

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 (Firefox, Firefox ESR, Thunderbird) to version 148 or 140.8 (ESR) respectively, or later. Deploy through enterprise patch management systems and verify successful installation.

Recommended fix High confidence

Firefox 148.0 / Firefox ESR 140.8.0 / Thunderbird 148.0 / Thunderbird ESR 140.8.0 (depending on product and release channel)

  1. Identify whether you are using Firefox standard release, Firefox ESR, Thunderbird standard release, or Thunderbird ESR
  2. For Firefox standard release users: Upgrade to Firefox 148.0 or later
  3. For Firefox ESR users: Upgrade to Firefox ESR 140.8.0 or later
  4. For Thunderbird standard release users: Upgrade to Thunderbird 148.0 or later
  5. For Thunderbird ESR users: Upgrade to Thunderbird ESR 140.8.0 or later
  6. Restart the application after upgrading to ensure the patched JavaScript Engine is loaded
Caveat Standard minor version upgrade with no expected breaking changes; standard Mozilla release migration considerations apply

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

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-2765 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2026-2765 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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