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FirefoxWeb browser · Mozilla

CVE-2026-4697

HIGH · 7.5 CVSS v3.1 Published 2026-03-24
Fix available
A fix is available. Upgrade to 140.9.0 / 149.0 or later.
See remediation →
84/100
Remediation priority · High
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: Web Codecs 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

This is a memory safety vulnerability in Mozilla's Web Codecs component caused by incorrect boundary conditions when processing audio/video data. Boundary condition errors typically indicate insufficient bounds checking when accessing arrays or buffers, potentially leading to out-of-bounds memory reads or writes that could be exploited for information disclosure or code execution.

MitigationUpdate to Firefox 149+, Firefox ESR 140.9+, Thunderbird 149+, or Thunderbird 140.9+ to obtain the patch. Avoid processing untrusted media files until updates are applied.

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

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
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 checks

Work through these to decide whether this CVE applies to you.

  1. Check Firefox version
    Go to Menu > Help > About Firefox, navigate to about:support, or run `firefox --version` in terminal
    Affected if Version is below 140.9.0 or between 141.0 and 148.x (not 149.0 or higher)
  2. Verify Web Codecs API status
    Navigate to about:config and search for the media.webcodecs.enabled preference
    Affected if Web Codecs is enabled (value is true) on an affected Firefox version
  3. Confirm build ID matches patched release
    Navigate to about:support and locate the 'Build ID' field; compare to Mozilla's security advisory release dates
    Affected if Build ID predates the security patch release date for your Firefox branch
  4. Identify Web Codecs usage in web content
    Review browser console logs or use developer tools to detect usage of VideoDecoder, AudioDecoder, VideoEncoder, or AudioEncoder interfaces in visited web pages
    Affected if Web Codecs API is being invoked by web content while running an affected Firefox version

You are affected if running Firefox below version 140.9.0 or between 141.0-148.x with Web Codecs enabled or accessible in your browser context.

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

Update to Firefox 149+, Firefox ESR 140.9+, Thunderbird 149+, or Thunderbird 140.9+ to obtain the patch. Avoid processing untrusted media files until updates are applied.

Recommended fix High confidence

Firefox 149 (regular release) or Firefox ESR 140.9; Thunderbird 149 or Thunderbird 140.9

  1. Identify the installed Firefox version by navigating to Menu > Help > About Firefox
  2. If running Firefox 140.x ESR (Extended Support Release), upgrade to Firefox ESR 140.9 or later
  3. If running Firefox regular release, upgrade to Firefox 149 or later
  4. For Thunderbird users, upgrade to Thunderbird 149 or Thunderbird 140.9 depending on the release channel
  5. Restart the application after upgrading
  6. Verify the fix by checking the version again at Menu > Help > About
Caveat Mozilla ESR releases follow a different update schedule with longer support periods; ensure compatibility with any enterprise policies or add-ons 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
  • Testing8.0 h
  • Review / QA4.0 h
18.0 hours of engineering $3,040
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,864.

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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-2026-4697 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