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FirefoxWeb browser · Mozilla

CVE-2023-6204

MEDIUM · 6.5 CVSS v3.1 Published 2023-11-21
Fix available
A fix is available. Upgrade to 115.5 / 115.5.0 or later.
See remediation →
72/100
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
On some systems—depending on the graphics settings and drivers—it was possible to force an out-of-bounds read and leak memory data into the images created on the canvas element. This vulnerability affects Firefox < 120, Firefox ESR < 115.5.0, and Thunderbird < 115.5.

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

Out-of-bounds read vulnerability in the HTML5 canvas element allows memory data leakage into rendered images on systems with specific graphics settings and drivers. Affects Firefox ESR and Thunderbird through version 115.4/115.4.0.

MitigationUpgrade to Firefox 120, Firefox ESR 115.5.0, or Thunderbird 115.5 or later to remediate the 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:< 120.0
Firefox EsrWeb browser
Affected:< 115.5.0
Debian LinuxOperating system
Affected:= 10.0= 11.0= 12.0
ThunderbirdApplication
Affected:< 115.5

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
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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 Mozilla product
    Check which Mozilla application is installed: run 'firefox --version' for Firefox, 'firefox-esr --version' for Firefox ESR, or 'thunderbird --version' for Thunderbird. On Windows, check Add/Remove Programs or the application's About dialog.
    Affected if Any of Firefox, Firefox ESR, or Thunderbird is installed
  2. Check Firefox version
    Run 'firefox --version' or open Firefox and navigate to Help > About Firefox. Compare the reported version number to the affected range of versions below 120.0.
    Affected if Firefox version is below 120.0 (e.g., 119.x or earlier)
  3. Check Firefox ESR version
    Run 'firefox-esr --version' or open Firefox ESR and navigate to Help > About Firefox ESR. Compare the reported version number to the affected range of versions below 115.5.0.
    Affected if Firefox ESR version is below 115.5.0 (e.g., 115.4.x or earlier)
  4. Check Thunderbird version
    Run 'thunderbird --version' or open Thunderbird and navigate to Help > About Thunderbird. Compare the reported version number to the affected range of versions below 115.5.
    Affected if Thunderbird version is below 115.5 (e.g., 115.4.x or earlier)
  5. Confirm canvas usage context
    This vulnerability affects the HTML5 canvas rendering feature. Any use of canvas-based web content or email content with embedded canvas could trigger the flaw. The vulnerability requires the canvas feature to be active, which is standard in these products.
    Affected if The application processes HTML5 canvas content (web pages or HTML emails with canvas elements) on a system with affected graphics drivers

A user is affected if they have Firefox below 120.0, Firefox ESR below 115.5.0, or Thunderbird below 115.5, and the system has specific graphics settings/drivers that trigger the out-of-bounds read during canvas rendering.

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 115.5 / 115.5.0 / 120.0 or later
Fixed in 115.5115.5.0120.0
Interim mitigation

Upgrade to Firefox 120, Firefox ESR 115.5.0, or Thunderbird 115.5 or later to remediate the vulnerability.

Recommended fix High confidence

Firefox 120.0+, Firefox ESR 115.5.0+, Thunderbird 115.5+

  1. Upgrade Firefox to version 120.0 or later
  2. Upgrade Firefox ESR to version 115.5.0 or later
  3. Upgrade Thunderbird to version 115.5 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
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,424.

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-2023-6204 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