FirefoxWeb browser · Mozilla
CVE-2016-9073
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 · uneditedWebExtensions can bypass security checks to load privileged URLs and potentially escape the WebExtension sandbox. This vulnerability affects Firefox < 50.
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 · moderate confidenceWebExtensions in Firefox versions prior to 50 contained a vulnerability allowing them to bypass security checks designed to prevent loading privileged URLs, potentially enabling escape from the WebExtension sandbox and unauthorized access to privileged browser operations.
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
< 50.0CVSS 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
- 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 checksWork through these to decide whether this CVE applies to you.
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Determine Firefox versionNavigate to Menu > Help > About Firefox, or enter 'about:support' in the address bar. The version number is displayed at the top of the page.Affected if The version shown is earlier than 50.0 (for example, 49.x, 48.x, etc.)
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Confirm WebExtension presenceEnter 'about:addons' in the address bar and review the list of installed extensions. Look for extensions that use the WebExtensions API (modern add-ons, not legacy XPI overlays).Affected if Any WebExtension-style add-ons are installed in a Firefox version below 50.0
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Check extension detailsClick on each extension in about:addons to view its details. WebExtensions typically have a manifest.json file and use APIs like 'browser.runtime' or 'browser.tabs'.Affected if Extensions using WebExtension APIs are present in Firefox versions below 50.0
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Verify extension permissionsIn the extension details (about:addons), review the permissions requested. Extensions with privileged browser operation permissions (such as 'tabs', 'webRequest', or 'nativeMessaging') indicate potential attack surface.Affected if Extensions with elevated permissions exist in Firefox versions below 50.0
You are affected if running any Mozilla Firefox version below 50.0 that has WebExtensions installed and enabled.
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 data50.0
Upgrade Firefox to version 50 or later to patch the vulnerability. In enterprise environments, verify that existing WebExtensions remain compatible with the updated version.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 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 $2,464.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-9073 — 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-2016-9073 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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