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FirefoxWeb browser · Mozilla

CVE-2026-4684

HIGH · 7.5 CVSS v3.1 Published 2026-03-24
Fix available
A fix is available. Upgrade to 115.34.0 / 140.9.0 or later.
See remediation →
82/100
Remediation priority · High
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
Race condition, use-after-free in the Graphics: WebRender component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

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

A race condition in Mozilla's WebRender graphics component leads to a use-after-free vulnerability. This occurs when the program attempts to access memory that has already been freed, potentially allowing arbitrary code execution or denial of service. The vulnerability has a CVSS score of 7.5 (HIGH) due to the potential for memory corruption.

MitigationApply the vendor-provided patches by updating affected installations to Firefox 149, Firefox ESR 115.34/140.9, Thunderbird 149, or Thunderbird 140.9, or later versions.

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:< 115.34.0< 149.0>= 128.0, < 140.9.0

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
High
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/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. Determine installed Firefox version
    Open Firefox, click the menu button (three horizontal lines), select Help, then About Firefox. The version number will display in the window that opens.
    Affected if The displayed version is less than 115.34.0, OR is 128.0 or higher but less than 140.9.0, OR is 149.0 or higher but less than 149.0 (which means any version below 149.0 that is not 115.34.0 or above is potentially affected)
  2. Confirm WebRender is enabled
    In the Firefox address bar, navigate to about:support. Look for the "Compositing" entry in the page and check if WebRender is listed as the backend.
    Affected if WebRender is listed as the active graphics compositor (this is the component with the vulnerability)
  3. Check for extended support release (ESR) version
    In about:support, look for the "Version" field. If it contains "ESR", note the full version number (for example, Firefox 115.x ESR).
    Affected if The ESR version is less than 115.34.0 or is 128.0 through 140.9.0 (older ESR branches before the patched versions)

A user is affected if their Firefox version falls within any of the vulnerable ranges and WebRender is the active compositor.

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 115.34.0 / 140.9.0 / 149.0 or later
Fixed in 115.34.0140.9.0149.0
Interim mitigation

Apply the vendor-provided patches by updating affected installations to Firefox 149, Firefox ESR 115.34/140.9, Thunderbird 149, or Thunderbird 140.9, or later versions.

Recommended fix High confidence

Firefox 149 (standard) or Firefox ESR 140.9 / Firefox ESR 115.34 (depending on your release channel)

  1. 1. Check the currently installed Firefox version by navigating to Menu > Help > About Firefox
  2. 2. If running Firefox 115.x (ESR), upgrade to Firefox ESR 115.34.0 or later
  3. 3. If running Firefox 128.x through 140.8.x (ESR), upgrade to Firefox ESR 140.9.0 or later
  4. 4. If running standard Firefox release prior to 149, upgrade to Firefox 149 or later
  5. 5. Alternatively, download the latest stable Firefox release from www.mozilla.org

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,390
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,224.

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-2026-4684 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