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FirefoxWeb browser · Mozilla

CVE-2020-15663

HIGH · 8.8 CVSS v3.1 Published 2020-10-01
Fix available
A fix is available. Upgrade to 68.12 / 78.2 or later.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges

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
If Firefox is installed to a user-writable directory, the Mozilla Maintenance Service would execute updater.exe from the install location with system privileges. Although the Mozilla Maintenance Service does ensure that updater.exe is signed by Mozilla, the version could have been rolled back to a previous version which would have allowed exploitation of an older bug and arbitrary code execution with System Privileges. *Note: This issue only affected Windows operating systems. Other operating systems are unaffected.*. This vulnerability affects Firefox < 80, Thunderbird < 78.2, Thunderbird < 68.12, Firefox ESR < 68.12, and Firefox ESR < 78.2.

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

The Mozilla Maintenance Service (a Windows service handling Firefox updates) runs updater.exe with SYSTEM privileges from the Firefox install directory. If Firefox is installed to a user-writable location (non-default), an attacker can replace the signed updater.exe with an older vulnerable version. The service only validates the Mozilla signature but not the executable version, allowing rollback attacks to exploit known bugs and achieve arbitrary code execution with SYSTEM privileges.

MitigationUpdate to Firefox >= 80, Thunderbird >= 78.2, or Firefox ESR >= 78.2; ensure Firefox is installed to the default protected directory (Program Files) rather than user-writable locations.

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:< 80.0>= 78.0, < 78.2
Firefox EsrWeb browser
Affected:>= 68.0, < 68.12
ThunderbirdApplication
Affected:>= 68.0, < 68.12>= 78.0, < 78.2

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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. Identify installed Mozilla products
    Check for Firefox or Thunderbird installation via registry key 'HKLM\SOFTWARE\Mozilla\Mozilla Firefox' or 'HKLM\SOFTWARE\Mozilla\Mozilla Thunderbird', or by listing directories in Program Files that contain 'Firefox' or 'Thunderbird'
    Affected if Either Firefox or Thunderbird is present on the system
  2. Determine installation directory
    Query the registry value 'InstallPath' under the product's registry key, or right-click the application in Add/Remove Programs to view the install location
    Affected if The installation path is NOT under 'C:\Program Files' or 'C:\Program Files (x86)' - for example, if installed to a user profile folder or custom user-writable location
  3. Check installed version against affected ranges
    Read the 'Version' value from the same registry key (e.g., HKLM\SOFTWARE\Mozilla\Mozilla Firefox\CurrentVersion) and compare: Firefox < 78.2, Firefox ESR < 68.12, Thunderbird < 68.12 or < 78.2
    Affected if The installed version falls within any of the affected ranges (Firefox < 78.2, Firefox ESR < 68.12, Thunderbird < 68.12 or < 78.2)
  4. Verify Mozilla Maintenance Service exists
    Open Services console (services.msc) and look for 'Mozilla Maintenance Service', or run 'sc query MozillaMaintenance' from command prompt
    Affected if The Mozilla Maintenance Service is installed and present on the system

A user is affected if Firefox or Thunderbird is installed to a user-writable directory (not Program Files), the installed version is vulnerable, and the Mozilla Maintenance Service exists on the system.

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 68.12 / 78.2 / 80.0 or later
Fixed in 68.1278.280.0
Interim mitigation

Update to Firefox >= 80, Thunderbird >= 78.2, or Firefox ESR >= 78.2; ensure Firefox is installed to the default protected directory (Program Files) rather than user-writable locations.

Fix this in Firefox Scoped from the published advisory
  • Consultation4.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,600
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,960.

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-2020-15663 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