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FirefoxWeb browser · Mozilla

CVE-2026-2779

CRITICAL · 9.8 CVSS v3.1 Published 2026-02-24
Fix available
A fix is available. Upgrade to 140.8.0 / 148.0 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
Incorrect boundary conditions in the Networking: JAR component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

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 memory safety vulnerability exists in Firefox and Thunderbird's Networking/JAR component due to incorrect boundary conditions. This flaw could allow an attacker to trigger out-of-bounds memory access when processing malicious JAR files, potentially leading to remote code execution. The issue affects multiple Mozilla products and was patched in the specified versions.

MitigationUpdate affected software to Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8 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:< 140.8.0< 148.0
ThunderbirdApplication
Affected:< 140.8.0< 148.0

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 products
    Check for Firefox or Thunderbird installations: On Windows check Program Files or %LOCALAPPDATA%\Mozilla\Firefox; On Linux check /usr/lib/firefox or /opt; On macOS check /Applications/Firefox.app or /Applications/Thunderbird.app. Also run 'firefox --version' or 'thunderbird --version' from command line.
    Affected if Either Firefox or Thunderbird is installed on the system
  2. Determine Firefox version
    Run 'firefox --version' or go to Firefox menu > Help > About Firefox to view the exact version number.
    Affected if Firefox version is below 140.8.0 or between 141.x and 147.x (any version < 148.0 but not 140.8.0+)
  3. Determine Thunderbird version
    Run 'thunderbird --version' or go to Thunderbird menu > Help > About Thunderbird to view the exact version number.
    Affected if Thunderbird version is below 140.8.0 or between 141.x and 147.x (any version < 148.0 but not 140.8.0+)
  4. Confirm JAR handling is active
    The JAR/Networking component processes JAR files automatically when Firefox or Thunderbird handles .jar file types or processes archives. This is enabled by default - no user configuration needed. Check if browser is used for general web browsing or email attachments.
    Affected if The product is used to access web content or process email attachments containing JAR files

You are affected if Firefox or Thunderbird is installed with any version below 140.8.0 or below 148.0, and the software processes web content or email that could include JAR files.

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 140.8.0 / 148.0 or later
Fixed in 140.8.0148.0
Interim mitigation

Update affected software to Firefox 148, Firefox ESR 140.8, Thunderbird 148, or Thunderbird 140.8 or later to remediate this vulnerability.

Recommended fix High confidence

Firefox 148 (or Firefox ESR 140.8) for Firefox users; Thunderbird 148 (or Thunderbird 140.8) for Thunderbird users

  1. Verify current Firefox or Thunderbird version by navigating to Menu > Help > About (or running firefox --version / thunderbird --version in terminal)
  2. Download Firefox 148 or Firefox ESR 140.8 from the official Mozilla website (www.mozilla.org)
  3. Download Thunderbird 148 or Thunderbird 140.8 from the official Mozilla website (www.mozilla.org)
  4. Close all instances of the application
  5. Install the downloaded version over the existing installation
  6. Restart the application
  7. Verify the installed version matches one of the fixed releases (140.8.0 or 148.0)

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
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

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-2026-2779 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