dbcve.org
FirefoxWeb browser · Mozilla

CVE-2026-6747

HIGH · 7.5 CVSS v3.1 Published 2026-04-21
Fix available
A fix is available. Upgrade to 140.10.0 / 150.0 or later.
See remediation →
84/100
Remediation priority · High
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 WebRTC 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 · high confidence

A use-after-free vulnerability exists in the WebRTC component of Firefox, Firefox ESR, and Thunderbird. This memory corruption issue allows attackers to potentially execute arbitrary code or cause denial of service by accessing freed memory through specially crafted WebRTC interactions.

MitigationUpdate affected installations to Firefox 150, Firefox ESR 140.10, Thunderbird 150, or Thunderbird 140.10. Deploy via enterprise patch management or direct user notification.

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
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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. Identify installed Mozilla product
    Check if Firefox or Thunderbird is installed by looking for the application in typical installation paths or running 'firefox --version' or 'thunderbird --version' in command line
    Affected if Either Firefox or Thunderbird is installed
  2. Determine Firefox version
    Run 'firefox --version' or navigate to 'about:firefox' in the browser address bar to view the installed version number
    Affected if Firefox version is below 140.10.0 or between 140.10.0 and 149.x (less than 150.0)
  3. Determine Firefox ESR version
    Run 'firefox --version' and check if it indicates ESR, or navigate to 'about:firefox' to view version details including ESR designation
    Affected if Firefox ESR version is below 140.10.0
  4. Determine Thunderbird version
    Run 'thunderbird --version' or navigate to 'about:thunderbird' in the application to view the installed version number
    Affected if Thunderbird version is below 140.10.0

You are affected if you have Firefox (any channel) below 140.10.0 or below 150.0, Firefox ESR below 140.10.0, or Thunderbird below 140.10.0, and WebRTC feature is enabled (which is the default state in these products).

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 installations to Firefox 150, Firefox ESR 140.10, Thunderbird 150, or Thunderbird 140.10. Deploy via enterprise patch management or direct user notification.

Recommended fix High confidence

Firefox 150 / Firefox ESR 140.10 / Thunderbird 150 / Thunderbird 140.10 (or later)

  1. Check current Firefox or Thunderbird version by navigating to Menu > Help > About (or using the 'firefox --version' or 'thunderbird --version' command in terminal)
  2. If running Firefox: Upgrade to Firefox 150 or later (or Firefox ESR 140.10 if using the ESR channel)
  3. If running Thunderbird: Upgrade to Thunderbird 150 or later (or Thunderbird 140.10)
  4. Restart the application after upgrade completes
  5. Verify the new version by checking Menu > Help > About
Caveat No breaking changes documented for these security updates; standard minor version upgrades within same release channel

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-2026-6747 — 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-2026-6747 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