FirefoxWeb browser · Mozilla
CVE-2026-4714
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 · uneditedIncorrect 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 · high confidenceMemory safety vulnerability in the Audio/Video component due to incorrect boundary condition checks. This could allow an attacker to read or write memory beyond allocated buffers through specially crafted media content, potentially leading to code execution or information disclosure.
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
< 140.9.0< 149.0CVSS 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
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 checksWork through these to decide whether this CVE applies to you.
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Check installed Firefox versionNavigate to Menu > Help > About Firefox, or enter 'about:support' in the address bar, or run 'firefox --version' from command lineAffected if The version displayed is below 140.9.0 or is between 141.0 and 148.x (inclusive)
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Identify Firefox release channelIn 'about:support' page, look at the 'Application Update Channel' field to determine if you are on Release, Beta, Nightly, or ESRAffected if Release and Beta channels below 149.0 are affected; ESR versions below 140.9.0 are affected
You are affected if your Firefox version is any release below 149.0 or any ESR release below 140.9.0, since the memory safety flaw exists in the Audio/Video component used for processing media content in those versions.
Generated from the published advisory. Verify against your own configuration.
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 · scoped140.9.0149.0
Update affected installations to Firefox 149+, Firefox ESR 140.9+, Thunderbird 149+, or Thunderbird 140.9+ to remediate this vulnerability.
Firefox 149 (or Firefox ESR 140.9 for enterprise deployments)
- Open Firefox and navigate to Menu > Help > About Firefox
- Click 'Check for Updates' or wait for the automatic update check
- If an update is available, click 'Update to Firefox 149' or 'Update to Firefox ESR 140.9'
- Restart Firefox after the update completes
- Alternatively, download the latest version directly from https://www.mozilla.org/firefox/ or https://www.mozilla.org/firefox/organizations/ for ESR
- Install the downloaded version and restart the browser
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-4714 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-4714 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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