FirefoxWeb browser · Mozilla
CVE-2019-11701
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 · uneditedThe default webcal: protocol handler will load a web site vulnerable to cross-site scripting (XSS) attacks. This default was left in place as a legacy feature and has now been removed. *Note: this issue only affects users with an account on the vulnerable service. Other users are unaffected.*. This vulnerability affects Firefox < 67.
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 confidenceFirefox contained a default webcal: protocol handler that would load external websites vulnerable to cross-site scripting (XSS) attacks. This legacy feature could allow an attacker with control over a webcal service to execute malicious scripts in the context of a user's session. Only users with accounts on the vulnerable webcal service were affected.
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
< 67.0CVSS 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
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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 Firefox version numberOpen Firefox and navigate to Help > About Firefox, or enter 'about:support' in the address bar. Locate the 'Version' field.Affected if The displayed version number is less than 67.0 (e.g., 66.x, 65.x, etc.)
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Verify webcal protocol handler presenceEnter 'about:config' in the address bar, accept the warning, then search for 'webcal' in the filter box. Look for any preference entries containing 'webcal' or 'webcal:' protocol handler registration.Affected if Any webcal-related protocol handler entries exist and are set to enabled or point to external URLs
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Check for calendar account configurationsReview browser settings or installed extensions for configured calendar accounts that use webcal: protocol (often found in calendar add-ons, Sync settings, or built-in calendar features).Affected if User has configured one or more webcal-based calendar accounts or subscriptions in the browser or connected services
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Confirm protocol handler allowlist statusEnter 'about:config' and search for 'protocol.security' or 'gecko.handlerService' preferences to check if protocol handler security restrictions are disabled or relaxed.Affected if Protocol handler security restrictions are disabled or set to allow untrusted handlers
A user is affected if their Firefox version is below 67.0 AND they have the webcal: protocol handler enabled, particularly if they use webcal-based calendar services.
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 data67.0
Upgrade Firefox to version 67 or later, which removes the legacy webcal: protocol handler. Alternatively, disable or restrict protocol handlers in browser settings.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 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-2019-11701 — 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-2019-11701 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
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