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FirefoxWeb browser · Mozilla

CVE-2023-6864

HIGH · 8.8 CVSS v3.1 Published 2023-12-19
Fix available
A fix is available. Upgrade to 115.6 / 121.0 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
Memory safety bugs present in Firefox 120, Firefox ESR 115.5, and Thunderbird 115.5. 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 < 115.6, Thunderbird < 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 · high confidence

Memory safety bugs in Firefox and Thunderbird allowed memory corruption that could potentially be exploited for arbitrary code execution. The vulnerabilities affected multiple components in Firefox versions prior to 121 and Firefox ESR/Thunderbird versions prior to 115.6.

MitigationUpgrade to Firefox 121+, Firefox ESR 115.6+, or Thunderbird 115.6+ to patch the memory safety vulnerabilities.

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
ThunderbirdApplication
Affected:< 115.6

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: On Linux (Debian), run 'dpkg -l | grep -E "firefox|thunderbird"'. On Windows, check Program Files. On macOS, check Applications folder.
    Affected if Either Firefox or Thunderbird is installed on the system
  2. Check Firefox version (non-ESR)
    In Firefox, navigate to Menu > Help > About Firefox, or enter 'about:support' in the address bar. The version number is displayed at the top. On Linux, run 'firefox --version' or 'dpkg -l firefox'.
    Affected if The installed version is below 121.0 (for example, 120.0, 119.0, etc.)
  3. Check Firefox ESR version
    In Firefox ESR, navigate to Menu > Help > About Firefox, or enter 'about:support' in the address bar. On Linux, run 'firefox-esr --version' or 'dpkg -l firefox-esr'.
    Affected if The installed version is below 115.6 (for example, 115.5, 115.4, etc.)
  4. Check Thunderbird version
    In Thunderbird, navigate to Menu > Help > About Thunderbird, or enter 'about:support' in the address bar. On Linux, run 'thunderbird --version' or 'dpkg -l thunderbird'.
    Affected if The installed version is below 115.6 (for example, 115.5, 115.4, etc.)

The environment is affected if any installed Firefox version is below 121.0, any Firefox ESR version is below 115.6, or any Thunderbird version is below 115.6.

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+, Firefox ESR 115.6+, or Thunderbird 115.6+ to patch the memory safety vulnerabilities.

Recommended fix High confidence

Firefox 121.0, Firefox ESR 115.6, Thunderbird 115.6

  1. For Firefox (Windows/macOS/Linux): Download and install Firefox 121.0 or later from https://www.mozilla.org/firefox/
  2. For Firefox ESR: Download and install Firefox ESR 115.6 or later from https://www.mozilla.org/firefox/organizations/
  3. For Thunderbird: Download and install Thunderbird 115.6 or later from https://www.thunderbird.net/
  4. For Debian Linux systems: Run 'apt-get update' followed by 'apt-get upgrade' to apply security updates for firefox-esr and thunderbird packages
  5. Restart the browser/application after upgrading to ensure the fix is fully applied

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
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

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-2023-6864 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