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FirefoxWeb browser · Mozilla

CVE-2025-10528

HIGH · 7.3 CVSS v3.1 Published 2025-09-16
Fix available
A fix is available. Upgrade to 140.3.0 / 143.0 or later.
See remediation →
82/100
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
Sandbox escape due to undefined behavior, invalid pointer in the Graphics: Canvas2D component. This vulnerability was fixed in Firefox 143, Firefox ESR 140.3, Thunderbird 143, and Thunderbird 140.3.

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 sandbox escape vulnerability exists in the Graphics: Canvas2D component of Firefox and Thunderbird due to undefined behavior causing an invalid pointer dereference. This could allow an attacker to break out of the sandboxed environment and potentially execute arbitrary code. The vulnerability was addressed in Firefox 143, Firefox ESR 140.3, Thunderbird 143, and Thunderbird 140.3.

MitigationApply the vendor-supplied patches by updating affected installations to Firefox 143 (or ESR 140.3) and Thunderbird 143 (or 140.3) 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:< 140.3.0< 143.0
ThunderbirdApplication
Affected:< 140.3.0>= 141.0, < 143.0

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
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

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 the installed product
    Check if Firefox or Thunderbird is installed. On Windows, look in Program Files. On macOS, check /Applications. On Linux, check package manager or which firefox thunderbird.
    Affected if The system has Firefox or Thunderbird installed
  2. Determine the installed Firefox version
    For Firefox: Enter 'about:support' in the address bar, or run 'firefox --version' from command line. Look for the version number in the 'Application Basics' section.
    Affected if Firefox version is less than 140.3.0 or is between 141.0 and 142.x (less than 143.0)
  3. Determine the installed Thunderbird version
    For Thunderbird: Enter 'about:support' in the address bar, or run 'thunderbird --version' from command line. Look for the version number.
    Affected if Thunderbird version is less than 140.3.0 or is between 141.0 and 142.x (less than 143.0)
  4. Verify the Canvas2D component is in use
    The vulnerability exists in the Graphics: Canvas2D component. This component is enabled by default in Firefox and Thunderbird for rendering web content and emails with graphics. No special configuration check needed - it is part of the standard rendering pipeline.
    Affected if The application processes HTML content, web pages, or email with graphical elements (standard use case)
  5. Confirm the sandbox is enabled
    The vulnerability is a sandbox escape. Check that the sandbox setting has not been disabled. In Firefox, go to about:config and search for 'security.sandbox.content.level' (default is non-zero). In Thunderbird, check similar settings.
    Affected if The sandbox is enabled (this is the default and required for the vulnerability to be a sandbox escape)

The user is affected if they have Firefox versions < 140.3.0, or 141.x through 142.x, or Thunderbird versions < 140.3.0 or 141.x through 142.x, with the Canvas2D component in use (standard configuration).

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 140.3.0 / 143.0 or later
Fixed in 140.3.0143.0
Interim mitigation

Apply the vendor-supplied patches by updating affected installations to Firefox 143 (or ESR 140.3) and Thunderbird 143 (or 140.3) or later versions.

Recommended fix High confidence

Firefox 143 (or Firefox ESR 140.3) / Thunderbird 143 (or Thunderbird 140.3)

  1. Check current Firefox or Thunderbird version via Help > About Firefox/Thunderbird
  2. Download Firefox 143 from www.mozilla.org (or Firefox ESR 140.3 if using the ESR channel)
  3. Download Thunderbird 143 from www.mozilla.org (or Thunderbird 140.3 if using the standard release)
  4. Install the downloaded version
  5. Restart the browser or email client to apply the update
Caveat Security updates are generally backward compatible; however, some add-ons or extensions may require updates for the new version

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.

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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-2025-10528 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