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FirefoxWeb browser · Mozilla

CVE-2026-4710

CRITICAL · 9.8 CVSS v3.1 Published 2026-03-24
Fix available
A fix is available. Upgrade to 140.9.0 / 149.0 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 Audio/Video component. This vulnerability was fixed in Firefox 149, 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

A boundary condition vulnerability in the Audio/Video component of Firefox, Firefox ESR, and Thunderbird allows incorrect memory access during media processing, likely enabling heap overflow or out-of-bounds write conditions that could lead to arbitrary code execution.

MitigationOrganizations should immediately deploy the fixed versions (Firefox 149, Firefox ESR 140.9, Thunderbird 149, Thunderbird 140.9) across all managed endpoints 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:< 140.9.0< 149.0
ThunderbirdApplication
Affected:< 140.9.0< 149.0

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 product
    Open the application and go to Help > About, or check the application name and installation location
    Affected if The system has Firefox, Firefox ESR, or Thunderbird installed
  2. Retrieve Firefox version
    Type about:firefox in the address bar and press Enter, or run 'firefox --version' from command line
    Affected if Version is displayed as less than 140.9.0 or less than 149.0
  3. Retrieve Thunderbird version
    Type about:thunderbird in the address bar and press Enter, or run 'thunderbird --version' from command line
    Affected if Version is displayed as less than 140.9.0 or less than 149.0
  4. Verify Firefox ESR version
    Type about:support in the address bar and check the version number under Application Basics, or run 'firefox-esr --version' from command line
    Affected if Version is displayed as less than 140.9.0 or less than 149.0

If the installed Firefox, Firefox ESR, or Thunderbird version is below 140.9.0 or below 149.0, the environment is affected by this vulnerability in the Audio/Video component.

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 140.9.0 / 149.0 or later
Fixed in 140.9.0149.0
Interim mitigation

Organizations should immediately deploy the fixed versions (Firefox 149, Firefox ESR 140.9, Thunderbird 149, Thunderbird 140.9) across all managed endpoints to remediate this critical vulnerability.

Recommended fix High confidence

Firefox 149 (stable) or Firefox ESR 140.9 (extended support); Thunderbird 149 or Thunderbird 140.9

  1. Check current Firefox version by navigating to Menu > Help > About Firefox (or entering 'about:firefox' in address bar)
  2. Check current Thunderbird version by navigating to Menu > Help > About Thunderbird (or entering 'about:thunderbird' in address bar)
  3. For Firefox: Download Firefox 149 (or Firefox ESR 140.9 for extended support release) from the official Mozilla website at www.mozilla.org
  4. For Thunderbird: Download Thunderbird 149 (or Thunderbird 140.9) from the official Mozilla website at www.mozilla.org
  5. Close all Firefox/Thunderbird instances and run the installer to complete the upgrade
  6. Verify the update was successful by checking the version again (should show 149.x or 140.9.x)
Caveat Standard Mozilla releases typically have minimal breaking changes; ESR versions recommended for organizations requiring stability

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.

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-2026-4710 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