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FirefoxWeb browser · Mozilla

CVE-2026-6769

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 Debugger 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 privilege escalation vulnerability exists in the Debugger component of Firefox and Thunderbird. An attacker could potentially exploit the debugger functionality to gain elevated privileges on the affected system. This issue was addressed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

MitigationUpdate Firefox to version 150 or later (or ESR 140.10+), and Thunderbird to version 150 or later (or ESR 140.10+) 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. Identify installed Mozilla product
    Check if Firefox or Thunderbird is installed. On Windows, look in Program Files/Mozilla Firefox or Program Files/Mozilla Thunderbird. On macOS, check /Applications/Firefox.app or /Applications/Thunderbird.app. On Linux, check which package is installed via package manager or locate the executable.
    Affected if Product is Firefox or Thunderbird and version is below 140.10.0 or between 140.10.0 and 149.x (for Firefox only)
  2. Determine Firefox version
    Open Firefox, go to Help > About Firefox, or navigate to about:support in the address bar. The version number is displayed on the page.
    Affected if Version is below 140.10.0 (ESR) or below 150.0 (non-ESR)
  3. Determine Thunderbird version
    Open Thunderbird, go to Help > About Thunderbird, or navigate to about:support in the address bar. The version number is displayed on the page.
    Affected if Version is below 140.10.0 or below 150.0 (if a 150.x non-ESR version exists)
  4. Verify Debugger feature availability
    In Firefox or Thunderbird, open the Developer Tools (F12 or Ctrl+Shift+I), then click on the Debugger tab. This confirms the debugger component is accessible in the browser/mail client.
    Affected if Debugger is accessible and the installed version is in the affected range (< 140.10.0 or < 150.0 for Firefox, < 140.10.0 for Thunderbird)
  5. Check for ESR version indicator
    In about:support, look for the version string. ESR versions contain 'ESR' in the version number (e.g., 140.10esr).
    Affected if Running an ESR version below 140.10 (e.g., 128.x ESR)

You are affected if you have Firefox below 140.10.0 ESR or below 150.0, or Thunderbird below 140.10.0, with the Debugger feature 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 140.10.0 / 150.0 or later
Fixed in 140.10.0150.0
Interim mitigation

Update Firefox to version 150 or later (or ESR 140.10+), and Thunderbird to version 150 or later (or ESR 140.10+) to remediate this vulnerability.

Recommended fix High confidence

Firefox 150+ / Firefox ESR 140.10+ / Thunderbird 150+ / Thunderbird 140.10+

  1. Open Firefox or Thunderbird
  2. Navigate to the application menu (three horizontal lines)
  3. Select 'Help' > 'About Firefox' or 'About Thunderbird'
  4. The application will check for updates automatically
  5. If an update is available, download and install version 150 or later (or version 140.10 for ESR/Thunderbird 140.x branch)
  6. Restart the application after the update completes

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

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-2026-6769 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