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FirefoxWeb browser · Mozilla

CVE-2018-12403

MEDIUM · 5.3 CVSS v3.0 Published 2019-02-28
Fix available
A fix is available. Upgrade to 63.0 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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 · unedited
If a site is loaded over a HTTPS connection but loads a favicon resource over HTTP, the mixed content warning is not displayed to users. This vulnerability affects 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 confidence

Firefox versions prior to 63 fail to display mixed content warnings when favicon resources are loaded over HTTP on HTTPS sites, allowing an attacker to load mixed content without alerting the user to the security risk.

MitigationUpgrade Firefox to version 63 or later to resolve the mixed content warning bypass.

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
Affected:< 63.0
Ubuntu LinuxOperating system
Affected:= 14.04= 16.04= 18.04= 18.10

CVSS 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
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Verify Firefox is installed
    Check for Firefox binary: `which firefox` or `ls /usr/bin/firefox*` on Linux systems. On Windows, check Program Files folder or registry.
    Affected if Firefox browser is present on the system
  2. Determine installed Firefox version
    Run `firefox --version` or `firefox -v` from command line. On Windows, right-click Firefox executable > Properties > Details tab for version.
    Affected if Version number returned is less than 63.0 (e.g., 62.0, 61.0, etc.)
  3. Confirm mixed content warning behavior (optional verification)
    Open any HTTPS website, then check network requests for HTTP favicon loads using browser DevTools (F12 > Network tab). Look for favicon.ico loaded via HTTP on an HTTPS page.
    Affected if HTTP favicon requests load without triggering a mixed content warning or security indicator in the address bar

A user is affected if Firefox version is installed and the version number is below 63.0, allowing mixed content favicons to load silently on HTTPS pages.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to 63.0 or later
Fixed in 63.0
Interim mitigation

Upgrade Firefox to version 63 or later to resolve the mixed content warning bypass.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,424.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2018-12403 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data