dbcve.org
FirefoxWeb browser · Mozilla

CVE-2018-18506

MEDIUM · 5.9 CVSS v3.1 Published 2019-02-05
Fix available
A fix is available. Upgrade to 65.0 or later.
See remediation →
68/100
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
When proxy auto-detection is enabled, if a web server serves a Proxy Auto-Configuration (PAC) file or if a PAC file is loaded locally, this PAC file can specify that requests to the localhost are to be sent through the proxy to another server. This behavior is disallowed by default when a proxy is manually configured, but when enabled could allow for attacks on services and tools that bind to the localhost for networked behavior if they are accessed through browsing. This vulnerability affects Firefox < 65.

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's proxy auto-detection (WPAD) feature allows PAC files to route localhost requests through a remote proxy, enabling remote attackers to intercept traffic intended for local services. This occurs because the security restriction that blocks localhost proxying in manual proxy configurations is not applied when proxy auto-detection is enabled.

MitigationUpgrade Firefox to version 65 or later, which enforces the localhost proxy restriction regardless of proxy configuration method.

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:< 65.0
Ubuntu LinuxOperating system
Affected:= 14.04= 16.04= 18.04= 18.10
Debian LinuxOperating system
Affected:= 8.0= 9.0
Enterprise LinuxOperating system
Affected:= 8.0
Enterprise Linux DesktopOperating system
Affected:= 6.0= 7.0
Enterprise Linux EusOperating system
Affected:= 8.1= 8.2= 8.4= 8.6
Enterprise Linux ServerOperating system
Affected:= 6.0= 7.0
Enterprise Linux Server AusOperating system
Affected:= 7.6= 8.2= 8.4= 8.6

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/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 checks

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

  1. Check Firefox version
    Open Firefox, go to Help > About Firefox, or run 'firefox --version' from command line, or check /usr/bin/firefox
    Affected if Version is below 65.0
  2. Check proxy configuration method
    Go to Firefox Preferences > Network Settings > Settings, or check for autoconfig URL in about:config (network.proxy.autoconfig_url)
    Affected if Proxy is set to 'Automatic proxy configuration URL' (PAC/WPAD) rather than 'No proxy' or manual proxy settings
  3. Identify configured PAC URL
    In Network Settings, note the URL in the 'Automatic proxy configuration URL' field, or check network.proxy.autoconfig_url in about:config
    Affected if A PAC URL is configured and points to a remote server (not localhost or a local file)

User is affected if Firefox version is below 65.0 AND proxy auto-detection (PAC/WPAD) is enabled with a remote PAC URL, allowing potential interception of localhost traffic.

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 65.0 or later
Fixed in 65.0
Interim mitigation

Upgrade Firefox to version 65 or later, which enforces the localhost proxy restriction regardless of proxy configuration method.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2018-18506 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2018-18506 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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