FirefoxWeb browser · Mozilla
CVE-2026-12327
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 · uneditedMemory safety bugs present in Firefox ESR 140.11, Thunderbird ESR 140.11, Firefox 151 and Thunderbird 151. 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 152, Firefox ESR 140.12, Thunderbird 152, 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 · high confidenceMemory safety bugs in Firefox ESR 140.11, Thunderbird ESR 140.11, Firefox 151, and Thunderbird 151 allowed memory corruption that could potentially be exploited for arbitrary code execution.
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
< 115.37.0< 152.0.0>= 140.0, < 140.12.0< 152.0.0>= 140.0, < 140.12.0CVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/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 checksWork through these to decide whether this CVE applies to you.
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Check Firefox versionOpen Firefox, go to Help > About Firefox, or navigate to about:support in the address bar. The version number is displayed at the top of the page.Affected if The version is 140.0 through 140.11.x (ESR), or 151.x, or any version below 152.0.0 (non-ESR)
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Check Thunderbird versionOpen Thunderbird, go to Help > About Thunderbird. The version number is displayed in the dialog window.Affected if The version is 140.0 through 140.11.x, or 151.x, or any version below 152.0.0
You are affected if Firefox or Thunderbird is installed with a version between 140.0 and 140.11.x (ESR or standard), or version 151.x, and you have not updated to 140.12+ or 152+ respectively.
Generated from the published advisory. Verify against your own configuration.
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 · scoped115.37.0140.12.0152.0.0
Update affected installations to Firefox 152, Firefox ESR 140.12, Thunderbird 152, or Thunderbird 140.12 to remediate the vulnerability.
Firefox 152, Firefox ESR 140.12, Thunderbird 152, or Thunderbird ESR 140.12 (depending on the branch in use)
- 1. Identify the currently installed Firefox or Thunderbird version by navigating to Menu > Help > About (or using the About dialog)
- 2. If running Firefox: Upgrade to version 152 or later for the main release, or Firefox ESR 140.12 or later for the ESR release
- 3. If running Thunderbird: Upgrade to version 152 or later for the main release, or Thunderbird ESR 140.12 or later for the ESR release
- 4. For older versions below 115.37.0, upgrade to the latest available version in the 115.x ESR branch (115.37.0 or later)
- 5. Restart the application after upgrading
- 6. Verify the upgrade was successful by checking the version in Menu > Help > About
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation2.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,744.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-12327 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-12327 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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