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FirefoxWeb browser · Mozilla

CVE-2026-6761

HIGH · 8.8 CVSS v3.1 Published 2026-04-21
Fix available
A fix is available. Upgrade to 140.10.0 / 150.0 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges

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 Networking component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

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 Networking component of Mozilla Firefox, Firefox ESR, and Thunderbird. The vulnerability allows an attacker to gain elevated privileges beyond the user's standard permissions, likely through manipulation of network request handling or socket operations.

MitigationUpdate affected software to Firefox 150, Firefox ESR 140.10, Thunderbird 150, or Thunderbird 140.10 or later 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:< 140.10.0< 150.0
ThunderbirdApplication
Affected:< 140.10.0

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 Firefox menu > Help > About Firefox, or enter 'about:support' in the address bar, or run 'firefox --version' from command line
    Affected if The displayed version is below 140.10.0 or is a version between 140.10.0 and 150.0 (for example 141.x through 149.x)
  2. Check installed Firefox ESR version
    Navigate to Firefox ESR menu > Help > About Firefox ESR, or run 'firefox --version' from command line
    Affected if The displayed version is below 140.10.0
  3. Check installed Thunderbird version
    Navigate to Thunderbird menu > Help > About Thunderbird, or enter 'about:support' in the address bar, or run 'thunderbird --version' from command line
    Affected if The displayed version is below 140.10.0
  4. Confirm networking functionality is in use
    The networking component is enabled by default in all affected products. Verify by attempting to load a webpage in the browser or checking that network connectivity works.
    Affected if Networking is functional (the vulnerability requires the networking component to be active)

You are affected if any installed Firefox, Firefox ESR, or Thunderbird version falls below 140.10.0, or if Firefox is between 140.10.0 and 150.0 (excluding 150.0 itself), and the networking component is active.

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 140.10.0 / 150.0 or later
Fixed in 140.10.0150.0
Interim mitigation

Update affected software to Firefox 150, Firefox ESR 140.10, Thunderbird 150, or Thunderbird 140.10 or later to remediate this vulnerability.

Recommended fix High confidence

Firefox 150 (or Firefox ESR 140.10), Thunderbird 140.10 (or Thunderbird 150)

  1. Check current Firefox or Thunderbird version via Help > About (or running 'firefox --version' / 'thunderbird --version' in terminal)
  2. For Firefox: Navigate to https://www.mozilla.org/firefox/ and download version 150 or later, or for ESR users download version 140.10 or later
  3. For Thunderbird: Navigate to https://www.thunderbird.net/ and download version 140.10 or later, or version 150 or later
  4. Install the updated version following standard installation procedures
  5. Restart the application and verify the version in Help > About
Caveat Standard minor version upgrades typically have no breaking changes; ensure any local add-ons are compatible

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

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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-2026-6761 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