FirefoxWeb browser · Mozilla
CVE-2019-9803
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 Upgrade-Insecure-Requests (UIR) specification states that if UIR is enabled through Content Security Policy (CSP), navigation to a same-origin URL must be upgraded to HTTPS. Firefox will incorrectly navigate to an HTTP URL rather than perform the security upgrade requested by the CSP in some circumstances, allowing for potential man-in-the-middle attacks on the linked resources. 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 · high confidenceFirefox fails to upgrade same-origin HTTP URLs to HTTPS when the Upgrade-Insecure-Requests (UIR) directive is set in Content Security Policy. Instead of performing the security upgrade as required by the UIR specification, Firefox incorrectly navigates to the HTTP URL, allowing man-in-the-middle attackers to intercept or modify the traffic.
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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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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Determine installed Firefox versionOpen Firefox, go to Help > About Firefox, or type 'about:support' in the address bar and look for the Version field. Alternatively, run 'firefox --version' from command line.Affected if Version is earlier than 66.0 (e.g., 65.0, 64.0, etc.)
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Identify CSP policies with UIR directiveReview web application configurations, HTTP headers, and meta tags for Content-Security-Policy headers containing 'upgrade-insecure-requests'. Check server configurations (Apache, Nginx, IIS) and application code for CSP rules.Affected if A Content-Security-Policy header includes the 'upgrade-insecure-requests' directive
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Verify same-origin HTTP URL handlingSet up a test page with CSP 'upgrade-insecure-requests' containing a same-origin HTTP link (e.g., <a href="http://example.com/page">). Load the page in the affected Firefox version and observe whether the navigation URL remains HTTP or is upgraded to HTTPS.Affected if The HTTP URL is NOT upgraded to HTTPS when clicked, staying on the HTTP version instead
A user is affected if running Firefox version earlier than 66.0 AND serving content with Content-Security-Policy that includes the upgrade-insecure-requests directive for same-origin HTTP URLs.
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 data66.0
Upgrade Firefox to version 66 or later to resolve this CSP bypass. Organizations should ensure automated browser updates are enabled or deploy the patched version through their patch management systems.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 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 $2,320.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2019-9803 — 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-2019-9803 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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