FirefoxWeb browser · Mozilla
CVE-2019-9815
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 · uneditedIf hyperthreading is not disabled, a timing attack vulnerability exists, similar to previous Spectre attacks. Apple has shipped macOS 10.14.5 with an option to disable hyperthreading in applications running untrusted code in a thread through a new sysctl. Firefox now makes use of it on the main thread and any worker threads. *Note: users need to update to macOS 10.14.5 in order to take advantage of this change.*. This vulnerability affects Thunderbird < 60.7, Firefox < 67, and Firefox ESR < 60.7.
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 confidenceA timing side-channel (Spectre-class) vulnerability in Firefox and Thunderbird that exploits hyperthreading to potentially extract sensitive information via cache timing attacks. The fix leverages a new macOS 10.14.5 sysctl that allows disabling hyperthreading for threads running untrusted 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
< 67.0
Firefox EsrWeb browser
< 60.7< 60.7CVSS 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
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/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 run 'firefox --version' from command lineAffected if Version is less than 67.0
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Check installed Firefox ESR versionOpen Firefox ESR, go to Help > About Firefox ESR, or run 'firefox-esr --version' from command lineAffected if Version is less than 60.7
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Check installed Thunderbird versionOpen Thunderbird, go to Help > About Thunderbird, or run 'thunderbird --version' from command lineAffected if Version is less than 60.7
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Verify operating system is macOSRun 'uname -s' or check System Preferences > About, the fix leverages an Apple-specific sysctlAffected if Operating system is NOT macOS (the mitigation is macOS-specific)
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Check if hyperthreading is enabledRun 'sysctl hw.physicalcpu hw.logicalcpu' on macOS; hyperthreading is enabled if logical CPUs is roughly double physical CPUsAffected if Hyperthreading is enabled (logical CPUs is approximately 2x physical CPUs)
User is affected if running Firefox < 67.0, Firefox ESR < 60.7, or Thunderbird < 60.7 on macOS with hyperthreading enabled, as the Apple sysctl mitigation cannot be applied to protect untrusted code threads.
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 data60.767.0
Update to macOS 10.14.5 or later and upgrade to Firefox 67+, Thunderbird 60.7+, or Firefox ESR 60.7+ to enable the hyperthreading mitigation via Apple's new sysctl for untrusted code threads.
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-2019-9815 — 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-2019-9815 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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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
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