FirefoxWeb browser · Mozilla
CVE-2026-6763
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 · uneditedMitigation bypass in the File Handling 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 confidenceA mitigation bypass in the File Handling component allows attackers to circumvent existing security controls. This appears to be a vulnerability where a previously mitigated file handling flaw could be re-exploited through a different attack vector.
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
< 140.10.0< 150.0>= 140.0, < 140.10.0CVSS 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
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Identify installed Mozilla productCheck if Firefox or Thunderbird is installed. On Windows, look in Program Files. On macOS, check /Applications. On Linux, check package manager or /usr/lib/firefox or /usr/lib/thunderbird.Affected if Neither Firefox nor Thunderbird is installed - not affected.
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Determine Firefox versionOpen Firefox, go to Menu > Help > About Firefox, or navigate to about:support. The version number is displayed.Affected if Version is < 140.10.0 or >= 140.10.0 but < 150.0 - affected.
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Determine Thunderbird versionOpen Thunderbird, go to Menu > Help > About Thunderbird, or navigate to about:support. The version number is displayed.Affected if Version is >= 140.0 and < 140.10.0 - affected.
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Check for Firefox ESRIf running Firefox ESR, the version format includes ESR (e.g., 140.10esr). Confirm via Menu > Help > About Firefox.Affected if Firefox ESR version < 140.10.0 - affected.
The environment is affected if Mozilla Firefox of any type is installed with version below 150.0, or Mozilla Thunderbird is installed with version >= 140.0 but below 140.10.0.
Generated from the published advisory. Verify against your own configuration.
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 · scoped140.10.0150.0
Upgrade to Firefox 150+, Firefox ESR 140.10+, Thunderbird 150+, or Thunderbird 140.10+ to obtain the patched version.
Firefox 150 (or Firefox ESR 140.10); Thunderbird 140.10
- 1. Back up your profile data (bookmarks, passwords, emails) before upgrading
- 2. Download Firefox 150 (or Firefox ESR 140.10 for enterprise/extended support needs) from the official Mozilla website
- 3. Download Thunderbird 140.10 from the official Mozilla website
- 4. Close all instances of Firefox and Thunderbird
- 5. Install the new version of Firefox by running the downloaded installer
- 6. Install the new version of Thunderbird by running the downloaded installer
- 7. Restart Firefox and Thunderbird after installation completes
- 8. Verify the installed version by checking Help > About Firefox / Thunderbird
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-6763 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-6763 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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.
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.
- 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