dbcve.org
FirefoxWeb browser · Mozilla

CVE-2026-6785

HIGH · 7.5 CVSS v3.1 Published 2026-04-26
Fix available
A fix is available. Upgrade to 115.35.0 / 140.10.0 or later.
See remediation →
82/100
Remediation priority · High
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
Memory safety bugs present in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 150, Firefox ESR 115.35, 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

Multiple memory safety bugs in Firefox ESR and Thunderbird allowed memory corruption. While the specific vulnerability type isn't detailed, memory safety issues in browsers typically involve buffer overflows, use-after-free, or similar defects that can be triggered via malicious web content to corrupt memory and potentially achieve arbitrary code execution.

MitigationUpgrade to Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, or Thunderbird 140.10 to obtain the patched versions.

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:< 115.35.0< 150.0>= 140.0, < 140.10.0
ThunderbirdApplication
Affected:>= 140.0, < 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
High
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/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 Firefox version
    Navigate to Firefox, click the menu icon (three horizontal lines), select Help, then About Firefox. The version number is displayed in the window that opens.
    Affected if Version is below 115.35.0, or is 140.0 through 140.9.x (versions 140.0 to less than 140.10.0), or is below 150.0 for versions 140.0 and above.
  2. Identify installed Thunderbird version
    In Thunderbird, click the menu button (three horizontal lines), select Help, then About Thunderbird. The version number appears in the dialog.
    Affected if Version is 140.0 or higher but below 140.10.0.
  3. Confirm product type for Firefox
    Check if the installation is Firefox (standard release) or Firefox ESR (Extended Support Release). In About Firefox, ESR versions display 'ESR' in the version string (e.g., '115.34.0 ESR').
    Affected if Both standard Firefox and Firefox ESR versions fall within the affected ranges listed in step 1.
  4. Verify vulnerability is applicable only if JavaScript is enabled
    This CVE involves memory corruption in the browser engine. The vulnerability can only be triggered when JavaScript is enabled in the browser settings.
    Affected if JavaScript is enabled in the browser (default state). Disabling JavaScript would prevent exploitation but does not change the affected version status.

Your installation is affected if it is Firefox version below 115.35.0, or between 140.0 and 140.9.x, or Thunderbird version 140.0 through 140.9.x.

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 115.35.0 / 140.10.0 / 150.0 or later
Fixed in 115.35.0140.10.0150.0
Interim mitigation

Upgrade to Firefox 150, Firefox ESR 115.35, Firefox ESR 140.10, Thunderbird 150, or Thunderbird 140.10 to obtain the patched versions.

Recommended fix High confidence

Firefox 150 (release) or Firefox ESR 115.35/140.10 (ESR); Thunderbird 150 or Thunderbird 140.10 (ESR)

  1. 1. Backup your current profile data (bookmarks, passwords, settings) as a precaution
  2. 2. Close all instances of Firefox or Thunderbird
  3. 3. Download the latest stable version from the official Mozilla website (www.mozilla.org) or use your system's package manager to update
  4. 4. Install the new version (Firefox 150 or Thunderbird 150 for release channels; Firefox ESR 115.35, Firefox ESR 140.10, or Thunderbird 140.10 for ESR channels)
  5. 5. Restart the application and verify the version by checking Help > About Firefox/Thunderbird
Caveat Minor: Some legacy extensions may be incompatible with the new major version; test critical extensions before production deployment

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
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-6785 — 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-2026-6785 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