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FirefoxWeb browser · Mozilla

CVE-2026-12330

MEDIUM · 5.4 CVSS v3.1 Published 2026-06-16
Fix available
A fix is available. Upgrade to 115.37.0 / 140.12.0 or later.
See remediation →
61/100
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
Incorrect boundary conditions in the Internationalization component. This vulnerability was fixed in Firefox ESR 140.12, Firefox ESR 115.37, and Thunderbird 140.12.

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 · low confidence

A boundary condition vulnerability exists in the Internationalization component of Firefox and Thunderbird. This type of flaw typically involves improper bounds checking when processing locale or character encoding data, potentially allowing controlled memory reads or writes. The CVSS 5.4 suggests limited impact requiring user interaction.

MitigationUpdate affected installations to Firefox ESR 140.12, Firefox ESR 115.37, or Thunderbird 140.12. Organizations should deploy these updates through their standard patch management processes.

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:< 115.37.0>= 140.0, < 140.12.0
ThunderbirdApplication
Affected:>= 140.0, < 140.12.0

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
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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. Identify installed Firefox version
    On Windows: Check Help > About Firefox or open about:support. On macOS: Use Firefox > About Firefox. On Linux: Run 'firefox --version' in terminal. Alternatively, check the program file properties for firefox.exe (Windows) or the application bundle (macOS).
    Affected if The version displayed is less than 115.37.0, or greater than or equal to 140.0 but less than 140.12.0
  2. Identify installed Thunderbird version
    On Windows: Check Help > About Thunderbird. On macOS: Use Thunderbird > About Thunderbird. On Linux: Run 'thunderbird --version' in terminal. Alternatively, check the program file properties for thunderbird.exe (Windows) or the application bundle (macOS).
    Affected if The version displayed is greater than or equal to 140.0 but less than 140.12.0

A user is affected if their installed Firefox version is below 115.37.0 or falls between 140.0 and 140.12.0 (inclusive of 140.0 up to but not including 140.12), or if their Thunderbird version is 140.0 through 140.11.x.

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 115.37.0 / 140.12.0 or later
Fixed in 115.37.0140.12.0
Interim mitigation

Update affected installations to Firefox ESR 140.12, Firefox ESR 115.37, or Thunderbird 140.12. Organizations should deploy these updates through their standard patch management processes.

Recommended fix High confidence

Firefox ESR 115.37, Firefox ESR 140.12, or Thunderbird 140.12 depending on current branch in use

  1. Check the current installed version of Firefox or Thunderbird by navigating to the application and selecting 'Help' > 'About Firefox' or 'About Thunderbird'
  2. If running Firefox ESR version 115.x, upgrade to Firefox ESR 115.37 or later
  3. If running Firefox ESR version 140.x, upgrade to Firefox ESR 140.12 or later
  4. If running Thunderbird version 140.x, upgrade to Thunderbird 140.12 or later
  5. Restart the application after the update completes
  6. Verify the installed version matches or exceeds the fixed releases (Firefox ESR 115.37+, Firefox ESR 140.12+, or Thunderbird 140.12+)
Caveat No breaking changes expected; this is a security patch release within the same major version branches

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
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
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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-2026-12330 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