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FirefoxWeb browser · Mozilla

CVE-2026-4698

CRITICAL · 9.8 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 →
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
JIT miscompilation in the JavaScript Engine: JIT 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

JIT (Just-In-Time) miscompilation vulnerability in the SpiderMonkey JavaScript engine's JIT component. The miscompilation could allow memory corruption or code execution during JavaScript execution.

MitigationUpdate to Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, or Thunderbird 140.9 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:< 115.34.0< 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
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 if Mozilla Firefox is installed
    Check for Firefox executable or application: On Windows, look in Program Files\Mozilla Firefox\; on macOS, check /Applications/Firefox.app; on Linux, run which firefox or check /usr/lib/firefox/
    Affected if Firefox is not installed on the system
  2. Determine the installed Firefox version number
    Open Firefox and navigate to Menu > Help > About Firefox, or type about:support in the address bar. Alternatively, check the executable version via command line: firefox --version (Linux) or inspect file properties of firefox.exe (Windows)
    Affected if The displayed version falls within affected ranges: < 115.34.0, < 149.0, or >= 128.0 to < 140.9.0
  3. Confirm the vulnerability applies to the JIT compiler
    The vulnerability is in the SpiderMonkey JIT compiler component. No specific configuration check needed - the flaw exists in the JIT compilation process itself when Firefox processes JavaScript. Verify JIT is active by loading any JavaScript-heavy webpage
    Affected if Firefox is running JavaScript with JIT compilation enabled (default state) and version is affected

A user is affected if Mozilla Firefox is installed with a version less than 115.34.0, less than 149.0, or between 128.0 and 140.8.x inclusive.

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

Update to Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, or Thunderbird 140.9 or later to remediate this vulnerability.

Recommended fix High confidence

Firefox 149 (main release), Firefox ESR 115.34 or Firefox ESR 140.9 (ESR branches), or Thunderbird 149/140.9

  1. Check current Firefox version via Help > About Firefox or running 'firefox --version'
  2. For Firefox 128.x and newer: upgrade to Firefox 140.9 or later
  3. For Firefox main release (48.x-148.x): upgrade to Firefox 149 or later
  4. For Firefox ESR 115.x and older: upgrade to Firefox ESR 115.34 or later
  5. If using Thunderbird: upgrade to Thunderbird 140.9 or 149 depending on version branch
Caveat ESR users should verify compatibility of add-ons with newer ESR branch if upgrading across major ESR versions; no known breaking changes for standard Firefox upgrades

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-2026-4698 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