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FirefoxWeb browser · Mozilla

CVE-2020-15683

CRITICAL · 9.8 CVSS v3.1 Published 2020-10-22
Fix available
A fix is available. Upgrade to 78.4 / 82.0 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 81 and Firefox ESR 78.3. 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 ESR < 78.4, Firefox < 82, and Thunderbird < 78.4.

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 81 and Firefox ESR 78.3 allowed memory corruption that could potentially be exploited for arbitrary code execution. The vulnerability affected multiple Mozilla products including Firefox, Firefox ESR, and Thunderbird.

MitigationUpgrade to Firefox ESR 78.4+, Firefox 82+, or Thunderbird 78.4+ to obtain the patched versions containing the memory safety fixes.

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:< 82.0
Firefox EsrWeb browser
Affected:< 78.4
Debian LinuxOperating system
Affected:= 9.0= 10.0
ThunderbirdApplication
Affected:< 78.4
LeapOperating system
Affected:= 15.1= 15.2

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 Firefox version (Windows/Mac/Linux GUI)
    Open Firefox, navigate to Help > About Firefox, or type 'about:firefox' in the address bar. The version number is displayed next to the Firefox logo.
    Affected if Version shown is less than 82.0 (for example 81.0, 80.x, etc.)
  2. Check Firefox ESR version (Windows/Mac/Linux)
    Open Firefox ESR, navigate to Help > About Firefox ESR, or type 'about:firefox' in the address bar. Look for the ESR designation in the version string.
    Affected if Version shown is less than 78.4 (for example 78.3, 78.2, etc.)
  3. Check Thunderbird version
    Open Thunderbird, navigate to Help > About Thunderbird, or type 'about:thunderbird' in the address bar.
    Affected if Version shown is less than 78.4 (for example 78.3, 78.2, etc.)
  4. Check installed package version on Linux (Debian/Ubuntu)
    Open terminal and run: dpkg -l | grep -E 'firefox|thunderbird' (Debian) or rpm -qa | grep -E 'firefox|thunderbird' (RPM-based).
    Affected if Package version listed is lower than 78.4 for ESR/Thunderbird or lower than 82.0 for standard Firefox.

A user is affected if their installed Firefox, Firefox ESR, or Thunderbird version is below 82.0, 78.4, or 78.4 respectively, as these contain the memory safety bug fixes.

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 78.4 / 82.0 or later
Fixed in 78.482.0
Interim mitigation

Upgrade to Firefox ESR 78.4+, Firefox 82+, or Thunderbird 78.4+ to obtain the patched versions containing the memory safety fixes.

Recommended fix High confidence

Firefox 82.0+, Firefox ESR 78.4+, Thunderbird 78.4+

  1. Identify which Mozilla product is in use (Firefox, Firefox ESR, or Thunderbird)
  2. Check the currently installed version of the product
  3. If using Firefox < 82.0, upgrade to Firefox 82.0 or later
  4. If using Firefox ESR < 78.4, upgrade to Firefox ESR 78.4 or later
  5. If using Thunderbird < 78.4, upgrade to Thunderbird 78.4 or later
  6. For Debian systems, apply vendor security updates: run 'apt update && apt upgrade' or 'apt-get update && apt-get upgrade' to receive the patched Mozilla packages
  7. Restart the browser/application after upgrading
Caveat Point release upgrades with minimal breaking changes; verify compatibility with existing extensions and configurations

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
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

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-2020-15683 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