FirefoxWeb browser · Mozilla
CVE-2019-9813
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 · uneditedIncorrect handling of __proto__ mutations may lead to type confusion in IonMonkey JIT code and can be leveraged for arbitrary memory read and write. This vulnerability affects Firefox < 66.0.1, Firefox ESR < 60.6.1, and Thunderbird < 60.6.1.
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 confidenceType confusion vulnerability in Mozilla's IonMonkey JIT compiler caused by incorrect handling of __proto__ property mutations. The flaw allows attackers to achieve arbitrary memory read and write operations by exploiting the type confusion in JIT-optimized JavaScript code.
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
< 60.6.1< 66.0.1< 60.6.1CVSS 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:3.0/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.
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Check installed Firefox versionOpen Firefox, go to Help > About Firefox, or navigate to about:support, or run: firefox --version from command lineAffected if Version is earlier than 60.6.1 (ESR branch) or earlier than 66.0.1 (regular release branch)
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Check installed Thunderbird versionOpen Thunderbird, go to Help > About Thunderbird, or run: thunderbird --version from command lineAffected if Version is earlier than 60.6.1
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Verify JavaScript JIT compilation is enabledIn Firefox address bar, type: about:config and press Enter. Search for: javascript.options.ion. Check if the value is set to true (enabled by default)Affected if The javascript.options.ion preference is set to true (JIT enabled)
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Confirm environment processes JavaScript contentDetermine if the browser or email client routinely loads or renders HTML emails, web content, or other untrusted JavaScript sourcesAffected if The application processes or has the ability to process JavaScript from untrusted sources
You are affected if you run an unpatched Firefox version (below 60.6.1 ESR or below 66.0.1) or Thunderbird version (below 60.6.1), with JIT compilation enabled, in an environment that can execute untrusted JavaScript content.
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 data60.6.166.0.1
Apply vendor-supplied security updates: Firefox 66.0.1 or later, Firefox ESR 60.6.1 or later, Thunderbird 60.6.1 or later. Prioritize updating systems that process untrusted JavaScript content.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 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 $2,560.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2019-9813 — 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-2019-9813 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
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- 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
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