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FirefoxWeb browser · Mozilla

CVE-2020-6809

HIGH · 7.5 CVSS v3.1 Published 2020-03-25
Fix available
A fix is available. Upgrade to 74.0 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
When a Web Extension had the all-urls permission and made a fetch request with a mode set to 'same-origin', it was possible for the Web Extension to read local files. This vulnerability affects Firefox < 74.

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

A Web Extension with 'all-urls' permission in Firefox could make a fetch request with mode set to 'same-origin' and read local files from the file system, bypassing same-origin restrictions.

MitigationUpgrade Firefox to version 74 or later to remediate this vulnerability.

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:< 74.0

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
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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, click the menu button (three horizontal lines), select Help, then About Firefox. Alternatively, navigate to about:support in the address bar.
    Affected if The displayed version number is less than 74.0 (for example, 73.x, 72.x, etc.)
  2. Identify extensions with all-urls permission
    Navigate to about:addons in Firefox, click the gear icon, select Manage Extension Shortcuts. Or install the Mozilla Add-on Validator to inspect extension permissions.
    Affected if A web extension is installed that requests the 'all-urls' permission (often listed as 'Access your data for all websites' in the extension description)
  3. Review extension fetch requests
    Open the Firefox Developer Tools (F12), go to the Console or Network tab, and observe any fetch() calls made by extensions with all-urls permission. Look for requests using mode: 'same-origin'.
    Affected if An extension with all-urls permission is making fetch requests with mode set to 'same-origin' to local file:// URLs

A user is affected if Firefox version is below 74.0 AND a web extension with all-urls permission is installed that uses fetch with same-origin mode to access local files.

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 74.0 or later
Fixed in 74.0
Interim mitigation

Upgrade Firefox to version 74 or later to remediate this vulnerability.

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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-2020-6809 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