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FirefoxWeb browser · Mozilla

CVE-2026-0879

CRITICAL · 9.8 CVSS v3.1 Published 2026-01-13
Fix available
A fix is available. Upgrade to 115.32.0 / 140.7.0 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
Sandbox escape due to incorrect boundary conditions in the Graphics component. This vulnerability was fixed in Firefox 147, Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

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 sandbox escape vulnerability exists in the Graphics component of Firefox and Thunderbird due to incorrect boundary conditions. This flaw allows an attacker to bypass the sandbox security boundary, potentially enabling arbitrary code execution with the privileges of the sandboxed process. The vulnerability is rated critical due to the potential for complete system compromise.

MitigationUpdate affected installations to Firefox 147, Firefox ESR 115.32/140.7, or Thunderbird 140.7 or later 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:< 115.32.0< 147.0>= 128.0, < 140.7.0
ThunderbirdApplication
Affected:< 140.7.0< 147.0

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
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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. Identify installed Mozilla Firefox version
    On Windows: Check Help > About Firefox or go to %ProgramFiles%\Mozilla Firefox\application.ini. On Linux: run 'firefox --version' or check /usr/lib/firefox/version.ini. On macOS: run 'firefox --version' or check /Applications/Firefox.app/Contents/Info.plist
    Affected if Version is below 115.32.0, or below 147.0, or falls between 128.0 and 140.7.0 inclusive
  2. Identify installed Mozilla Thunderbird version
    On Windows: Check Help > About Thunderbird or go to %ProgramFiles%\Mozilla Thunderbird\application.ini. On Linux: run 'thunderbird --version' or check /usr/lib/thunderbird/version.ini. On macOS: run 'thunderbird --version' or check /Applications/Thunderbird.app/Contents/Info.plist
    Affected if Version is below 140.7.0 or below 147.0
  3. Confirm Graphics component is in use
    The vulnerability exists in the Graphics component. This component is loaded by default in Firefox and Thunderbird when rendering web content or email content with graphics. No specific config check required as this is the default behavior.
    Affected if Firefox or Thunderbird is running and rendering graphical content (default state)

User is affected if they have Firefox version < 115.32.0 OR < 147.0 OR (>= 128.0 and < 140.7.0), OR Thunderbird version < 140.7.0 or < 147.0, and are using the browser to render graphical content (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 115.32.0 / 140.7.0 / 147.0 or later
Fixed in 115.32.0140.7.0147.0
Interim mitigation

Update affected installations to Firefox 147, Firefox ESR 115.32/140.7, or Thunderbird 140.7 or later to remediate this vulnerability.

Recommended fix High confidence

Firefox ESR 115.32.0 / Firefox ESR 140.7.0 / Firefox 147 / Thunderbird 140.7.0 / Thunderbird 147

  1. 1. Identify the currently installed Firefox or Thunderbird version via Help > About (or running 'firefox --version' or 'thunderbird --version' in terminal)
  2. 2. Determine which Firefox ESR branch (115.x or 128.x/140.x) or regular Firefox branch is in use
  3. 3. Download the appropriate fixed version from the official Mozilla website: https://www.mozilla.org/firefox/releases/ or https://www.mozilla.org/thunderbird/releases/
  4. 4. For Firefox ESR 115.x users: upgrade to Firefox ESR 115.32.0 or later
  5. 5. For Firefox users on 128-140.x branch: upgrade to Firefox ESR 140.7.0 or later
  6. 6. For Firefox users on regular channel: upgrade to Firefox 147 or later
  7. 7. For Thunderbird users: upgrade to Thunderbird 140.7.0 or later (or Thunderbird 147)
  8. 8. Restart the application after upgrade
Caveat Standard ESR channel provides longer support; verify compatibility with existing extensions and enterprise policies before upgrading

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
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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-2026-0879 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