dbcve.org
FirefoxWeb browser · Mozilla

CVE-2023-6865

MEDIUM · 6.5 CVSS v3.1 Published 2023-12-19
Fix available
A fix is available. Upgrade to 115.6 / 121.0 or later.
See remediation →
72/100
Remediation priority · Elevated
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
`EncryptingOutputStream` was susceptible to exposing uninitialized data. This issue could only be abused in order to write data to a local disk which may have implications for private browsing mode. This vulnerability affects Firefox ESR < 115.6 and Firefox < 121.

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 · moderate confidence

The `EncryptingOutputStream` component in Firefox contained a vulnerability where uninitialized memory data could be written to the local disk during encryption operations. This exposure could affect data written during private browsing sessions, potentially leaking sensitive information through uninitialized buffer contents.

MitigationUpgrade to Firefox 121 or later (or Firefox ESR 115.6 or later) to obtain the patched version that properly initializes buffers before writing encrypted data to disk.

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:< 121.0
Firefox EsrWeb browser
Affected:< 115.6
Debian LinuxOperating system
Affected:= 10.0= 11.0= 12.0

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
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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. Determine installed Firefox version
    Open Firefox, go to Help > About Firefox (or navigate to about:support) to view the exact version number
    Affected if Version is below 121.0 (e.g., 120.x or earlier)
  2. Check if running Firefox ESR
    In about:support, look for the 'Build ID' or 'Version' field - ESR versions include 'ESR' in the version string (e.g., 115.5 ESR)
    Affected if Running Firefox ESR version below 115.6 while using private browsing or encryption features
  3. Verify Windows/macOS/Linux package version via command line
    Windows: Check 'C:\Program Files\Mozilla Firefox\firefox.exe' properties or run 'firefox --version'. macOS: Run '/Applications/Firefox.app/Contents/MacOS/firefox --version' in Terminal. Linux: Run 'firefox --version' or check package with 'dpkg -l | grep firefox'
    Affected if Reported version number is less than 121.0 for regular Firefox or less than 115.6 for ESR
  4. Confirm Debian system version if applicable
    Run 'cat /etc/debian_version' or 'lsb_release -a' to identify the Debian release
    Affected if System runs Debian 10, 11, or 12 and has an unpatched Firefox package installed

You are affected if your Firefox version is below 121.0 (or below 115.6 for ESR) and you use private browsing or any feature that utilizes the EncryptingOutputStream component for disk encryption.

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 115.6 / 121.0 or later
Fixed in 115.6121.0
Interim mitigation

Upgrade to Firefox 121 or later (or Firefox ESR 115.6 or later) to obtain the patched version that properly initializes buffers before writing encrypted data to disk.

Recommended fix High confidence

Firefox 121.0 or Firefox ESR 115.6

  1. For Firefox users: Update to Firefox 121.0 or later via the application's built-in update mechanism or by downloading from www.mozilla.org
  2. For Firefox ESR users: Update to Firefox ESR 115.6 or later via the application's built-in update mechanism or by downloading from www.mozilla.org
  3. For Debian Linux systems: Run 'apt update' and 'apt upgrade' to apply available security patches, or specifically upgrade the firefox-esr package

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

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2023-6865 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2023-6865 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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