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FirefoxWeb browser · Mozilla

CVE-2026-4686

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 →
84/100
Remediation priority · High
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
Incorrect boundary conditions in the Graphics: Canvas2D 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 · moderate confidence

This is a client-side browser vulnerability in Mozilla's Graphics: Canvas2D component involving incorrect boundary conditions. Such flaws typically allow improper memory access during canvas rendering operations, potentially leading to out-of-bounds reads or writes that could be exploited for information disclosure or code execution.

MitigationUpgrade affected installations to Firefox 149+, Firefox ESR 115.34+, Firefox ESR 140.9+, Thunderbird 149+, or Thunderbird 140.9+ as listed in the official advisory.

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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. Check Firefox version number
    Open Firefox, click the menu button (three horizontal lines), select Help, then select About Firefox. The version number is displayed at the top of the window.
    Affected if The displayed version is less than 115.34.0, or is between 128.0 and 140.8.x inclusive, or is less than 149.0 (depending on which release channel you are on)
  2. Verify Canvas2D is enabled
    In the Firefox address bar, type about:config and press Enter. Search for the preference named canvas.imageCache.enabled or verify that the Canvas2D rendering feature is operational by default (it is enabled by default in unaltered Firefox installations).
    Affected if Canvas2D rendering is enabled (this is the default state; the vulnerability affects rendering operations when this feature is active)
  3. Confirm you are using standard Firefox
    Check if you are running Firefox (not Firefox ESR or Thunderbird) by looking at the About window - it will simply say Firefox if it is the standard release.
    Affected if You are running standard Firefox and your version falls within the affected ranges listed above

You are affected if your Firefox version is below 115.34.0, is between 128.0 and 140.8.x, or is below 149.0 and Canvas2D rendering is enabled (the default state).

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

Upgrade affected installations to Firefox 149+, Firefox ESR 115.34+, Firefox ESR 140.9+, Thunderbird 149+, or Thunderbird 140.9+ as listed in the official advisory.

Recommended fix High confidence

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

  1. Check current Firefox version via Help > About Firefox
  2. For Firefox versions < 115.34.0 on ESR 115.x: upgrade to Firefox ESR 115.34
  3. For Firefox versions < 149.0 on standard release: upgrade to Firefox 149
  4. For Firefox versions >= 128.0 and < 140.9.0: upgrade to Firefox ESR 140.9
  5. Restart Firefox after upgrade
  6. Verify the fix by checking Help > About Firefox shows the corrected version number

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
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,696.

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-2026-4686 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