FirefoxWeb browser · Mozilla
CVE-2019-9805
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 · uneditedA latent vulnerability exists in the Prio library where data may be read from uninitialized memory for some functions, leading to potential memory corruption. This vulnerability affects Firefox < 66.
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 memory corruption vulnerability exists in the Prio library where certain functions read data from uninitialized memory, potentially allowing attackers to leak or corrupt memory contents. This stems from the library failing to properly initialize memory buffers before use in specific functions.
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
< 66.0CVSS 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/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 and navigate to Help > About Firefox, or enter 'about:support' in the address bar and locate the 'Version' field in the page that loadsAffected if The displayed version number is less than 66.0 (for example, 65.x, 64.x, etc.)
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Check if Prio feature is enabled in FirefoxEnter 'about:config' in the address bar, accept the warning, then search for the preference named 'toolkit.prio.enable' or 'prio.enabled'Affected if The preference exists and is set to true, indicating the Prio library is actively being used
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Check for Prio library usage in third-party applicationsSearch the application or system for files named 'libprio' or 'prio.dll' (Windows), 'libprio.so' (Linux), or 'libprio.dylib' (macOS), or inspect application dependencies for Prio library linkageAffected if The application bundles or links to the Prio library and the library version is older than the patched version (contact the application vendor for specific version information)
A user is affected if they are running Firefox version below 66.0 with Prio telemetry enabled, or any application using an unpatched version of the Prio library.
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 · scoped66.0
Update Firefox to version 66 or later, which contains the patched Prio library. For applications using the Prio library directly, update to a patched version of the library that addresses the uninitialized memory read.
Firefox 66.0
- Upgrade Firefox to version 66.0 or later
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2019-9805 — 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-2019-9805 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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