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FirefoxWeb browser · Mozilla

CVE-2026-2770

CRITICAL · 9.8 CVSS v3.1 Published 2026-02-24
Fix available
A fix is available. Upgrade to 115.33.0 / 140.8.0 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
Use-after-free in the DOM: Bindings (WebIDL) component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, 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 · high confidence

A use-after-free vulnerability exists in the DOM Bindings (WebIDL) component of Firefox and Thunderbird. This memory corruption flaw allows an attacker to potentially execute arbitrary code by manipulating object lifecycle in the WebIDL bindings layer.

MitigationUpdate affected installations to Firefox 148, Firefox ESR 115.33/140.8, or Thunderbird 148/140.8 or later to remediate this critical 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:< 115.33.0< 148.0>= 128.0, < 140.8.0
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. Check if Firefox is installed
    On Windows: look for Firefox in Program Files or check the registry at HKLM\SOFTWARE\Mozilla\Mozilla Firefox\CurrentVersion. On Linux: run 'which firefox' or check /usr/lib/firefox. On macOS: check /Applications/Firefox.app
    Affected if Firefox is present on the system
  2. Check if Thunderbird is installed
    On Windows: look for Thunderbird in Program Files or check the registry at HKLM\SOFTWARE\Mozilla\Thunderbird\CurrentVersion. On Linux: run 'which thunderbird' or check /usr/lib/thunderbird. On macOS: check /Applications/Thunderbird.app
    Affected if Thunderbird is present on the system
  3. Determine Firefox version
    Run 'firefox --version' from command line, or on Windows open Help > About Firefox, or read the version from the registry key HKLM\SOFTWARE\Mozilla\Mozilla Firefox\CurrentVersion
    Affected if The installed version is < 115.33.0, OR >= 128.0 AND < 140.8.0, OR >= 148.0 but < 148.0 (check against all ranges)
  4. Determine Thunderbird version
    Run 'thunderbird --version' from command line, or on Windows open Help > About Thunderbird, or read the version from the registry key HKLM\SOFTWARE\Mozilla\Thunderbird\CurrentVersion
    Affected if The installed version is < 140.8.0 OR < 148.0 (check against all ranges)

You are affected if Firefox is installed with a version less than 115.33.0, or between 128.0 and 140.8.0 exclusive, or less than 148.0; OR if Thunderbird is installed with a version less than 140.8.0 or less than 148.0.

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 115.33.0 / 140.8.0 / 148.0 or later
Fixed in 115.33.0140.8.0148.0
Interim mitigation

Update affected installations to Firefox 148, Firefox ESR 115.33/140.8, or Thunderbird 148/140.8 or later to remediate this critical vulnerability.

Recommended fix High confidence

Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 140.8, or Thunderbird 148 (depending on your release channel)

  1. Check current Firefox or Thunderbird version via Help > About (or running 'firefox --version' / 'thunderbird --version' in terminal)
  2. For Firefox: Navigate to https://www.mozilla.org/firefox/all/ and download version 148 (or ESR 115.33 or ESR 140.8 depending on your release channel needs)
  3. For Thunderbird: Navigate to https://www.thunderbird.net/ and download version 140.8 or 148
  4. Close all Firefox/Thunderbird instances
  5. Run the installer and follow the prompts to complete the upgrade
  6. Restart the application and verify the version matches the expected fixed release
Caveat Major version upgrades may deprecate old extensions or features; review Mozilla release notes for breaking changes 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
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.

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-2026-2770 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