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FirefoxWeb browser · Mozilla

CVE-2026-2782

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. The Netmonitor is a developer tool for monitoring network requests. This flaw allows an attacker to elevate privileges, likely by escaping the sandbox restrictions of the Netmonitor. The vulnerability carries a critical CVSS score of 9.8.

MitigationUpdate affected systems to Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8 to remediate this 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:< 140.8.0< 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 a terminal and run 'firefox --version' or check for Firefox in your applications.
    Affected if Firefox is present on the system
  2. Check if Thunderbird is installed
    Open a terminal and run 'thunderbird --version' or check for Thunderbird in your applications.
    Affected if Thunderbird is present on the system
  3. Determine installed Firefox version
    In Firefox, navigate to about:support or go to Help > About Firefox. The version is displayed on the page.
    Affected if The displayed version is less than 140.8.0 or less than 148.0
  4. Determine installed Thunderbird version
    In Thunderbird, navigate to Help > About Thunderbird. The version is displayed on the page.
    Affected if The displayed version is less than 140.8.0 or less than 148.0
  5. Identify Netmonitor access
    Open the developer tools (press F12 or Ctrl+Shift+I), then click on the Network tab. Alternatively, navigate to about:netmonitor in the address bar.
    Affected if The Netmonitor interface loads successfully (indicating the vulnerable component is accessible)

A user is affected if they have Firefox or Thunderbird installed with a version lower than 140.8.0 or lower than 148.0, and the Netmonitor developer tool is accessible.

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 systems to Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8 to remediate this vulnerability.

Recommended fix High confidence

Firefox 148.x, Firefox ESR 140.8.x, Thunderbird 148.x, or Thunderbird ESR 140.8.x (depending on release channel used)

  1. Check current Firefox or Thunderbird version via Menu > Help > About (or thunderbird > About Thunderbird on Mac)
  2. For Firefox users: Download and install Firefox 148 or later from www.mozilla.org/firefox/download/
  3. For Firefox ESR users: Download and install Firefox ESR 140.8.0 or later from www.mozilla.org/firefox/download/
  4. For Thunderbird users: Download and install Thunderbird 148 or later from www.mozilla.org/thunderbird/download/
  5. For Thunderbird ESR users: Download and install Thunderbird 140.8.0 or later from www.mozilla.org/thunderbird/download/
  6. Restart the browser or email client after installation
Caveat Minor risk - Mozilla security point releases typically contain no breaking changes; always backup profile data before major updates

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
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.

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-2026-2782 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