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FirefoxWeb browser · Mozilla

CVE-2018-5135

HIGH · 7.5 CVSS v3.0 Published 2018-06-11
Fix available
A fix is available. Upgrade to 59.0 or later.
See remediation →
84/100
Remediation priority · High
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
WebExtensions can bypass normal restrictions in some circumstances and use "browser.tabs.executeScript" to inject scripts into contexts where this should not be allowed, such as pages from other WebExtensions or unprivileged "about:" pages. This vulnerability affects Firefox < 59.

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 WebExtensions API allowed browser.tabs.executeScript to bypass context restrictions and inject scripts into privileged contexts including pages from other WebExtensions and unprivileged about: pages. This is a privilege escalation flaw where extension scripts could execute in contexts they should be excluded from.

MitigationUpgrade Firefox to version 59 or later to receive the patch that enforces proper context restrictions on WebExtensions API calls.

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:< 59.0

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
High
Availability
None

CVSS:3.0/AV:N/AC:L/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 navigate to about:support) to view the installed version number
    Affected if The installed version is any version prior to 59.0 (e.g., 58.x, 57.x, or earlier)
  2. Identify WebExtensions with script injection capabilities
    Review installed extensions for any that use the browser.tabs.executeScript API or have 'tabs' permission in their manifest.json
    Affected if One or more WebExtensions with tabs.executeScript capability are installed on a Firefox version below 59.0
  3. Check for multiple coexisting extensions
    Review the list of installed add-ons/extensions in the Firefox Add-ons Manager (about:addons)
    Affected if Multiple extensions are installed, creating the condition where one extension could inject scripts into another extension's context

A user is affected if they are running any Firefox version below 59.0 and have WebExtensions installed that utilize the tabs.executeScript API, allowing potential cross-extension script injection.

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 59.0 or later
Fixed in 59.0
Interim mitigation

Upgrade Firefox to version 59 or later to receive the patch that enforces proper context restrictions on WebExtensions API calls.

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.

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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-2018-5135 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