FirefoxWeb browser · Mozilla
CVE-2018-12396
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 vulnerability where a WebExtension can run content scripts in disallowed contexts following navigation or other events. This allows for potential privilege escalation by the WebExtension on sites where content scripts should not be run. This vulnerability affects Firefox ESR < 60.3 and Firefox < 63.
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 WebExtension content script sandboxing bypass where content scripts can execute in contexts where they should be restricted following navigation or other events, enabling privilege escalation on sites where scripts shouldn't run.
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
< 63.0
Firefox EsrWeb browser
< 60.3
Debian LinuxOperating system
= 8.0= 9.0
Ubuntu LinuxOperating system
= 14.04= 16.04= 18.04= 18.10
Enterprise Linux DesktopOperating system
= 6.0= 7.0
Enterprise Linux ServerOperating system
= 6.0= 7.0
Enterprise Linux Server AusOperating system
= 7.6
Enterprise Linux Server EusOperating system
= 7.6CVSS 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
- None
- Integrity
- High
- Availability
- None
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
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 versionRun 'firefox --version' or go to Firefox menu > Help > About Firefox to view the exact version numberAffected if The version is less than 63.0 for standard Firefox or less than 60.3 for Firefox ESR
-
Confirm Firefox ESR version if applicableRun 'firefox --version' and look for 'ESR' in the output, or check the version string includes 'ESR'Affected if Running Firefox ESR version less than 60.3
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Identify WebExtension content scripts in useExamine installed extensions in Firefox: navigate to 'about:addons', review each extension's type and look for those with content scripts defined in their manifest.json filesAffected if Extensions with content scripts are installed and the Firefox version is vulnerable
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Check browser configuration for extension loadingNavigate to 'about:config' and check 'extensions.webextensions.restrictedDomains' or similar settings that control where extensions can runAffected if Extensions are allowed to run and the browser version is unpatched
You are affected if you are running Firefox standard version below 63.0 or Firefox ESR below 60.3 and have WebExtensions with content scripts installed.
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 data60.363.0
Update Firefox to version 60.3 or later (ESR) or version 63 or later to enforce proper content script context restrictions.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 h
- Testing1.0 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 $1,200.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-12396 — 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-2018-12396 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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