FirefoxWeb browser · Mozilla
CVE-2019-11730
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 exists where if a user opens a locally saved HTML file, this file can use file: URIs to access other files in the same directory or sub-directories if the names are known or guessed. The Fetch API can then be used to read the contents of any files stored in these directories and they may uploaded to a server. It was demonstrated that in combination with a popular Android messaging app, if a malicious HTML attachment is sent to a user and they opened that attachment in Firefox, due to that app's predictable pattern for locally-saved file names, it is possible to read attachments the victim received from other correspondents. This vulnerability affects Firefox ESR < 60.8, Firefox < 68, and Thunderbird < 60.8.
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 file: URI Same-Origin bypass in Firefox and Thunderbird allows locally-saved malicious HTML files to use the Fetch API to read and exfiltrate other files in the same or subdirectories. When a user opens a malicious HTML attachment, it can enumerate and upload known/guessed filenames from adjacent directories.
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
< 68.0
Firefox EsrWeb browser
< 60.8
Debian LinuxOperating system
= 8.0< 60.8= 15.0= 15.1all versionsCVSS 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
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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 versionRun 'firefox --version' or go to Help > About Firefox to see the installed version numberAffected if Version is below 68.0 (or below 60.8 for ESR)
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Check Thunderbird versionRun 'thunderbird --version' or go to Help > About Thunderbird to see the installed version numberAffected if Version is below 60.8
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Identify if untrusted HTML attachments are handledCheck email client or file browser settings for handling .html files; review whether users receive or open HTML email attachments or download HTML files from the internetAffected if Users open or process untrusted HTML attachments in the affected application
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Verify Same-Origin policy for file:// URIsCreate a test HTML file with 'fetch("file:///etc/passwd")' and open it in the browser; check if the request succeeds or is blocked by Same-Origin policyAffected if The Fetch request to a local file succeeds from a locally-opened HTML file, indicating the bypass is present
A user is affected if they run Firefox below 68.0 (or ESR below 60.8) or Thunderbird below 60.8 AND open a malicious HTML attachment that uses Fetch API to read files from adjacent directories.
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 data60.868.0
Upgrade to Firefox 68+, Firefox ESR 60.8+, or Thunderbird 60.8+. Avoid opening untrusted HTML attachments in Firefox until patched.
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-2019-11730 — 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-2019-11730 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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