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FirefoxWeb browser · Mozilla

CVE-2020-12389

CRITICAL · 10.0 CVSS v3.1 Published 2020-05-26
Fix available
A fix is available. Upgrade to 68.8.0 / 76.0 or later.
See remediation →
100/100
Remediation priority · Urgent
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
The Firefox content processes did not sufficiently lockdown access control which could result in a sandbox escape. *Note: this issue only affects Firefox on Windows operating systems.*. This vulnerability affects Firefox ESR < 68.8 and Firefox < 76.

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 content processes on Windows had insufficient access control restrictions, allowing a sandbox escape where malicious content could break out of the sandboxed content process and potentially execute code with elevated privileges.

MitigationUpgrade Firefox to version 76 or later (or Firefox ESR to 68.8 or later) on all Windows systems to apply the security patch that properly locks down access control in content processes.

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:< 76.0
Firefox EsrWeb browser
Affected:< 68.8.0

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
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

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. Confirm Windows platform
    Check if the system is running Windows (this vulnerability affects only Windows systems)
    Affected if Running any version of Firefox on non-Windows systems is not affected by this specific flaw
  2. Find installed Firefox version
    Open Firefox, click the menu button (three horizontal lines), select Help, then About Firefox. The version number will display in the window that opens.
    Affected if The installed version is below 76.0 (for standard Firefox) or below 68.8.0 (for Firefox ESR)
  3. Verify Firefox ESR status
    In the About Firefox window, look for 'Firefox ESR' in the version string. If it says just 'Firefox' without ESR, it is the standard release.
    Affected if Running Firefox ESR versions below 68.8.0 on Windows
  4. Confirm content process sandbox is enabled
    This vulnerability is a sandbox escape, so the content process sandbox must be active for exploitation to be relevant. Default Firefox installations on Windows enable content sandboxing.
    Affected if Content process sandbox is enabled (default state) on affected Firefox versions

The environment is affected if Firefox (or Firefox ESR) version below 76.0 (or 68.8.0 respectively) is running on Windows with the content process sandbox enabled.

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.

dbcve · scoped
Upgrade available Upgrade to 68.8.0 / 76.0 or later
Fixed in 68.8.076.0
Interim mitigation

Upgrade Firefox to version 76 or later (or Firefox ESR to 68.8 or later) on all Windows systems to apply the security patch that properly locks down access control in content processes.

Recommended fix High confidence

Firefox 76.0 or later / Firefox ESR 68.8.0 or later

  1. Back up bookmarks, passwords, and preferences (optional but recommended)
  2. Navigate to the official Mozilla Firefox download page at https://www.mozilla.org/firefox/
  3. Download Firefox 76.0 or later (or Firefox ESR 68.8.0 or later for ESR users)
  4. Run the installer and follow the prompts to install the updated version
  5. Restart Firefox after installation completes
  6. Verify the version by navigating to Help > About Firefox to confirm the update installed successfully

Generated from the published advisory — verify against the referenced sources before acting.

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

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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-2020-12389 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