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FirefoxWeb browser · Mozilla

CVE-2020-12396

CRITICAL · 9.8 CVSS v3.1 Published 2020-05-26
Fix available
A fix is available. Upgrade to 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
Mozilla developers and community members reported memory safety bugs present in Firefox 75. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects 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

Memory safety bugs in Firefox versions before 76 allow memory corruption that can potentially be exploited for arbitrary code execution. The vulnerability stems from improper memory handling in the browser's rendering engine or JavaScript components.

MitigationUpgrade Firefox to version 76 or later to apply the vendor patch addressing these memory safety issues.

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

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
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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. Check if Firefox is installed
    On Windows: Check for Firefox in Program Files or via registry. On macOS: Check /Applications/Firefox.app. On Linux: Run 'which firefox' or check package manager.
    Affected if Firefox is not found on the system (not affected)
  2. Locate Firefox executable and identify installation path
    Windows: Look in C:\Program Files\Mozilla Firefox\ or C:\Program Files (x86)\Mozilla Firefox\. macOS: Check /Applications/Firefox.app/Contents/MacOS/firefox. Linux: Common paths include /usr/bin/firefox or /opt/firefox/firefox.
    Affected if Cannot locate Firefox installation directory
  3. Retrieve installed Firefox version number
    Windows: Run 'firefox --version' from the Firefox directory, or right-click firefox.exe > Properties > Details tab. macOS: Run '/Applications/Firefox.app/Contents/MacOS/firefox --version' in Terminal. Linux: Run 'firefox --version' or 'rpm -q firefox' / 'dpkg -l firefox'.
    Affected if Command fails or returns no version
  4. Compare installed version against CVE threshold
    Compare the obtained version number to 76.0. Versions below 76.0 (such as 75.x, 74.x, etc.) are affected. Version 76.0 and above are not affected.
    Affected if Installed version is below 76.0 (e.g., 75.0, 74.0, 73.0, etc.)

If Firefox is installed and its version is below 76.0, the environment is affected by this memory corruption vulnerability.

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 76.0 or later
Fixed in 76.0
Interim mitigation

Upgrade Firefox to version 76 or later to apply the vendor patch addressing these memory safety issues.

Recommended fix High confidence

Firefox 76.0 or later

  1. Check current Firefox version: Open Firefox, go to Help > About Firefox, or run 'firefox --version' in terminal
  2. If version is less than 76.0, download Firefox 76.0 or later from the official Mozilla website (www.mozilla.org)
  3. Install the new version, allowing it to overwrite the existing installation
  4. Restart Firefox after installation completes
  5. Verify the fix by checking Help > About Firefox shows version 76.0 or higher
Caveat Minimal risk; security patch升级 typically compatible with existing profiles and extensions

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

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.

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-2020-12396 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