FirefoxWeb browser · Mozilla
CVE-2020-12406
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 · uneditedMozilla Developer Iain Ireland discovered a missing type check during unboxed objects removal, resulting in a crash. We presume that with enough effort that it could be exploited to run arbitrary code. This vulnerability affects Thunderbird < 68.9.0, Firefox < 77, and Firefox ESR < 68.9.
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 confidenceMissing type check during unboxed objects removal in the SpiderMonkey JavaScript engine causes a crash. This type confusion vulnerability could potentially be exploited to achieve arbitrary code execution with sufficient effort.
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
< 77.0
Firefox EsrWeb browser
< 68.9.0
Ubuntu LinuxOperating system
= 16.04= 18.04= 19.10= 20.04< 68.9.0CVSS 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
- 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 checksWork through these to decide whether this CVE applies to you.
-
Check Firefox versionRun 'firefox --version' or navigate to Firefox menu > Help > About Firefox to see the installed version numberAffected if Version is less than 77.0 (for regular Firefox) or less than 68.9.0 (for Firefox ESR)
-
Check Thunderbird versionRun 'thunderbird --version' or navigate to Thunderbird menu > Help > About Thunderbird to see the installed version numberAffected if Version is less than 68.9.0
-
Check Firefox package version on UbuntuRun 'dpkg -l | grep firefox' or 'apt policy firefox' to list the installed Firefox package versionAffected if Package version corresponds to Firefox versions below 77.0 (regular) or below 68.9.0 (ESR)
-
Confirm SpiderMonkey usageThis vulnerability is in the SpiderMonkey JavaScript engine bundled with Firefox and Thunderbird. No separate check needed - if the product version is affected, the engine is affected.Affected if The product version falls within the affected ranges
You are affected if Mozilla Firefox is below 77.0 (or below 68.9.0 for ESR), or Thunderbird is below 68.9.0, or Ubuntu Firefox packages are at vulnerable versions.
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.
From vendor data68.9.077.0
Update affected Mozilla products to fixed versions: Thunderbird to 68.9.0 or higher, Firefox to 77 or higher, or Firefox ESR to 68.9 or higher.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-12406 — 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-2020-12406 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