dbcve.org
FirefoxWeb browser · Mozilla

CVE-2026-2780

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
Privilege escalation in the Netmonitor 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 · moderate confidence

A privilege escalation vulnerability exists in the Netmonitor component of Firefox and Thunderbird. Netmonitor is a developer tool used for inspecting network requests. The vulnerability allows an attacker to gain elevated privileges through the component, potentially executing arbitrary code or accessing sensitive data. This is a critical flaw requiring immediate patching.

MitigationApply the security update by upgrading to Firefox 148 or later, Firefox ESR 140.8 or later, Thunderbird 148 or later, or Thunderbird 140.8 or later. In enterprise environments, deploy the updates via standard software distribution mechanisms.

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 installed Firefox version
    Navigate to menu > Help > About Firefox, or enter 'about:firefox' in the address bar. Note the full version number displayed.
    Affected if The version is below 140.8.0, or is 140.8.0 through 147.x
  2. Check installed Thunderbird version
    Navigate to menu > Help > About Thunderbird. Note the full version number displayed.
    Affected if The version is below 140.8.0, or is 140.8.0 through 147.x
  3. Verify Developer Tools access in Firefox
    Open a new tab, press F12 or Ctrl+Shift+I (Cmd+Option+I on Mac), or navigate to menu > More Tools > Developer Tools. Confirm the Developer Tools window opens.
    Affected if Developer Tools are enabled and accessible to the user
  4. Verify Developer Tools access in Thunderbird
    Navigate to menu > Tools > Developer Tools > Network Monitor, or press Ctrl+Shift+Q (Cmd+Option+Q on Mac).
    Affected if Developer Tools and Netmonitor are available in the installation
  5. Check if DevTools are restricted via enterprise policy
    Look for policies.json or mozilla.cfg files in the installation directory, or check about:support for Enterprise Policies Active.
    Affected if No enterprise policies are enforcing DevTools restrictions, meaning the feature is accessible

You are affected if you run Firefox or Thunderbird versions below 148.0 (or below 140.8.0 for ESR branches) AND have Developer Tools/Netmonitor accessible to local users on the system.

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

Apply the security update by upgrading to Firefox 148 or later, Firefox ESR 140.8 or later, Thunderbird 148 or later, or Thunderbird 140.8 or later. In enterprise environments, deploy the updates via standard software distribution mechanisms.

Recommended fix High confidence

Firefox 148 (or Firefox ESR 140.8); Thunderbird 148 (or Thunderbird ESR 140.8)

  1. Check current Firefox or Thunderbird version by navigating to Menu > Help > About (or running: firefox --version or thunderbird --version)
  2. For Firefox: Navigate to https://www.mozilla.org/firefox/ and download version 148.0 or later, or version 140.8.0 or later for ESR
  3. For Thunderbird: Navigate to https://www.mozilla.org/thunderbird/ and download version 148.0 or later, or version 140.8.0 or later
  4. Close all browser/email instances and run the installer
  5. Restart the application and verify the version in Menu > Help > About shows 148.x or 140.8.x or higher
  6. Alternatively, use the built-in update mechanism: Menu > Help > Check for Updates (or Help > About Thunderbird > Check for Updates)
Caveat No breaking changes documented for this security fix; standard upgrade applies

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

Fix this in Firefox Scoped from the published advisory
  • Consultation6.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,730
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,368.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-2780 — 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-2026-2780 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