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FirefoxWeb browser · Mozilla

CVE-2025-0243

MEDIUM · 5.1 CVSS v3.1 Published 2025-01-07
Fix available
A fix is available. Upgrade to 128.6.0 / 133.0 or later.
See remediation →
56/100
Remediation priority · Elevated
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
Memory safety bugs present in Firefox 133, Thunderbird 133, Firefox ESR 128.5, and Thunderbird 128.5. 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 was fixed in Firefox 134, Firefox ESR 128.6, Thunderbird 134, and Thunderbird 128.6.

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

Memory safety bugs in Firefox 133, Thunderbird 133, Firefox ESR 128.5, and Thunderbird 128.5 allowed memory corruption that could potentially be exploited for arbitrary code execution with sufficient effort.

MitigationUpgrade to Firefox 134, Firefox ESR 128.6, Thunderbird 134, or Thunderbird 128.6 to remediate these 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:< 128.6.0< 133.0
ThunderbirdApplication
Affected:< 128.6.0>= 129.0, < 134.0

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
Local
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/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. Check installed Firefox version
    In Firefox, navigate to Menu > Help > About Firefox. The version number will be displayed. Alternatively, enter 'about:support' in the address bar and look for the 'Version' field under 'Application Basics'. On command line, run 'firefox --version' or check your package manager's installed packages.
    Affected if The installed version is below 128.6.0 (for ESR) or below 133.0 (for regular Firefox)
  2. Check installed Thunderbird version
    In Thunderbird, navigate to Menu > Help > About Thunderbird. The version number will be displayed. Alternatively, enter 'about:support' in the address bar and look for the 'Version' field. On command line, run 'thunderbird --version' or check your package manager's installed packages.
    Affected if The installed version is below 128.6.0, or between 129.0 and 133.x inclusive (specifically below 134.0)
  3. Identify Firefox release channel
    In 'about:support', check the 'Release Channel' field. It will indicate whether you are running 'release', 'beta', 'dev', or 'esr' (Extended Support Release).
    Affected if The release channel is affected (ESR 128.5 or earlier, or regular release before 133.0)
  4. Verify exact version against ranges
    Compare your exact version number to: Firefox < 128.6.0 or < 133.0; Thunderbird < 128.6.0 or >= 129.0 and < 134.0. If your version exactly matches 128.6.0, 133.0, 134.0, or 128.6.0 ESR, you are NOT in the affected range.
    Affected if Your version falls within any of the affected version ranges and is not one of the patched versions (128.6.0, 133.0, 134.0, or ESR 128.6)

You are affected if either Firefox or Thunderbird is installed and the installed version is lower than the patched versions (Firefox 133.0 or ESR 128.6.0, Thunderbird 134.0 or 128.6.0).

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 128.6.0 / 133.0 / 134.0 or later
Fixed in 128.6.0133.0134.0
Interim mitigation

Upgrade to Firefox 134, Firefox ESR 128.6, Thunderbird 134, or Thunderbird 128.6 to remediate these memory safety vulnerabilities.

Recommended fix High confidence

Firefox 134, Firefox ESR 128.6, Thunderbird 134, or Thunderbird 128.6 (depending on current branch)

  1. Check current Firefox or Thunderbird version via Help > About (or running 'firefox --version' / 'thunderbird --version' in terminal)
  2. If running Firefox 133.x, upgrade to Firefox 134
  3. If running Firefox ESR 128.5.x, upgrade to Firefox ESR 128.6
  4. If running Thunderbird 133.x, upgrade to Thunderbird 134
  5. If running Thunderbird 128.5.x, upgrade to Thunderbird 128.6
  6. Restart the application after upgrade
  7. Verify version via Help > About to confirm the fix is applied
Caveat Minor: Some browser extensions or add-ons may need updates for compatibility with the new version

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-2025-0243 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