Ubuntu LinuxOperating system · Canonical
CVE-2018-5163
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 a malicious attacker has used another vulnerability to gain full control over a content process, they may be able to replace the alternate data resources stored in the JavaScript Start-up Bytecode Cache (JSBC) for other JavaScript code. If the parent process then runs this replaced code, the executed script would be run with the parent process' privileges, escaping the sandbox on content processes. This vulnerability affects Firefox < 60.
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 confidenceThis is a sandbox escape vulnerability in Firefox where an attacker who has already compromised a content process via another vulnerability can inject malicious code into the JavaScript Start-up Bytecode Cache (JSBC). When the parent process executes this poisoned bytecode, it runs with full parent process privileges, breaking the content process sandbox.
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
Ubuntu LinuxOperating system
= 14.04= 16.04= 17.10= 18.04
FirefoxWeb browser
< 60.0CVSS 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
- 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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Verify Firefox is installedCheck for Firefox executable: which firefox or ls /usr/bin/firefoxAffected if Firefox is not found on the system, the system is not affected by this specific Firefox vulnerability
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Check installed Firefox versionRun firefox --version or about:firefox in browser address barAffected if Version is less than 60.0 (e.g., 59.x, 58.x, etc.) indicates the browser is within the affected version range
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Confirm JSBC bytecode cache is in useInspect user profile directory for jsbc files: ls ~/.mozilla/firefox/*.default/*.jsbc 2>/dev/null || ls ~/.cache/mozilla/firefox/*.default/startupCache/*.jsbc 2>/dev/nullAffected if JSBC files exist in the profile, meaning the JavaScript Start-up Bytecode Cache feature is active and the vulnerability could be triggered
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Check if Firefox has been run with content processesReview crash reports in ~/.mozilla/firefox/*.default/crashreports/ or check process list for running firefox content processes: ps aux | grep -i firefox | grep -i contentAffected if Firefox has been actively used, indicating content processes have been spawned and JSBC may have been populated
A system is affected if Firefox version is below 60.0 and the browser has been run, enabling the JavaScript Start-up Bytecode Cache which the attacker would poison to escape the sandbox.
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 data60.0
Upgrade Firefox to version 60 or later. Until then, minimize exposure by restricting browser usage and avoiding untrusted content.
Fix this in Ubuntu Linux
Scoped from the published advisory
- Consultation8.0 h
- Implementation40.0 h
- Testing24.0 h
- Review / QA16.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $24,448.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-5163 — 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-2018-5163 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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- Version or environment caveats, and links to real fixes
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