dbcve.org
FirefoxWeb browser · Mozilla

CVE-2026-12315

CRITICAL · 9.1 CVSS v3.1 Published 2026-06-16
Fix available
A fix is available. Upgrade to 140.12.0 / 152.0.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable 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
Mitigation bypass in the DOM: Security component. 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 · moderate confidence

A mitigation bypass vulnerability in a Firefox/Thunderbird DOM security component, allowing attackers to circumvent existing security protections. The specific component and exploitation details are not disclosed in available sources.

MitigationApply the vendor-supplied patches: Upgrade to Firefox 152+, Firefox ESR 140.12+, Thunderbird 152+, or Thunderbird 140.12+ to remediate this vulnerability.

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:< 140.12.0< 152.0.0
ThunderbirdApplication
Affected:< 140.12.0< 152.0.0

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
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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, go to Menu > Help > About Firefox, or enter 'about:support' in the address bar and look for the 'Version' field under 'Application Basics'
    Affected if Version is below 140.12.0 OR version is 141.x-151.x (i.e., any version below 152.0.0 that is not 140.12.0 or higher)
  2. Check installed Thunderbird version
    In Thunderbird, go to Menu > Help > About Thunderbird, or enter 'about:support' in the address bar and look for the 'Version' field under 'Application Basics'
    Affected if Version is below 140.12.0 OR version is 141.x-151.x (i.e., any version below 152.0.0 that is not 140.12.0 or higher)
  3. Verify if using Firefox ESR channel
    In 'about:support', check the 'Build Configuration' section for 'Update Channel' - ESR builds will show 'esr' in the version string or update channel
    Affected if If ESR channel and version is below 140.12.0
  4. Confirm DOM security component is in use
    This vulnerability affects DOM security components - no specific config check needed as it is a component-level issue present in standard installations
    Affected if Running any affected version of Firefox or Thunderbird means the component contains the vulnerability

You are affected if your Firefox or Thunderbird version is any release below 152.0.0, or any ESR version below 140.12.0.

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 140.12.0 / 152.0.0 or later
Fixed in 140.12.0152.0.0
Interim mitigation

Apply the vendor-supplied patches: Upgrade to Firefox 152+, Firefox ESR 140.12+, Thunderbird 152+, or Thunderbird 140.12+ to remediate this vulnerability.

Recommended fix High confidence

Firefox 152 (or Firefox ESR 140.12); Thunderbird 152 (or Thunderbird 140.12)

  1. 1. Check the current version of Firefox by navigating to menu > Help > About Firefox (or typing 'about:support' in the address bar)
  2. 2. Check the current version of Thunderbird by navigating to menu > Help > About Thunderbird
  3. 3. If the installed version is below 140.12.0 or below 152.0.0, proceed with upgrade
  4. 4. For Firefox: Download Firefox 152 or later from www.mozilla.org or use the built-in update mechanism (menu > Help > About Firefox > Check for updates)
  5. 5. For Thunderbird: Download Thunderbird 152 or later from www.mozilla.org or use the built-in update mechanism (menu > Help > About Thunderbird > Check for updates)
  6. 6. Restart the application after the update completes
  7. 7. Verify the version has been updated to 140.12.0 or later, or 152.0.0 or later

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
3.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-12315 — 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-2026-12315 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